Optical display system and method with optical shifting of pixel position including conversion of pixel layout to form delta to stripe pattern by time base multiplexing

ABSTRACT

An optical display system and method selectively displaces delta triad pixels vertically. The first raster line of picture information is removed from the video signal, and each subsequent raster line of picture information (data) is displaced upward. Next, the entire picture is optically displaced down by a distance equal to one vertical pixel pitch placing the picture back in its original vertical position, but horizontal position of the pixels has changed. Thus picture information is displaced horizontally a distance equal to one and one half times horizontal pixel pitch. Odd pixel rows are displaced in one direction, and even pixel rows are displaced in the opposite direction. The technique can be used to double pixel density and, thus, resolution, in the horizontal direction by the selective shifting technique and coordination with the input video signals. Two views of a picture alternate at the frame rate fast enough to fuse them into a single image, and two successive frames are combined over time to act as a single super frame. This is time based multiplexing of a spatial pattern. Thus, a composite picture is formed using a strip pixel pattern with twice the horizontal pixel density of the original delta pattern. The triads in the first half of this super frame may partially overlap the triads in the second half of the super frame. This technique can be applied to either progressive or interlace scan formats.

[0001] The present invention relates generally, as is indicated, tooptical display system and method, active and passive dithering usingbirefringence, color image superpositioning, and display enhancementwith phase coordinated polarization switching. The present inventionalso relates to dithering systems for optical displays and methods, and,more particularly, to passive dithering systems and methods for changingthe location of an optical signal and for improving an optical display.The present invention also relates to the enhancing of optical displaysand methods to enhance such displays, and, more particularly, toenhancing optical displays and methods by coordinating the phase ofswitching light with the dynamic operation of the displayed imagedeveloping device.

BACKGROUND

[0002] Dithering systems have been used in a number of technologies inthe past. The objective of a dithering system is to change acharacteristic of a particular signal in a periodic (or random) fashionin order to provide a useful output. As is described in further detail,the dithering system of the invention may be used to change the relativelocation of an optical signal.

[0003] The present invention may be used with various types of displaysand systems. Exemplary displays are a CRT (sometimes referred to hereinas cathode ray tube) display, a liquid crystal display (sometimesreferred to herein as “LCD”), especially those which modulate lighttransmitted therethrough, reflective liquid crystal displays, lightemitting displays, such as electroluminescent displays, plasma displaysand so on.

[0004] Conventional optical displays typically display graphic visualinformation, such as computer generated graphics, and pictures generatedfrom video signals, such as from a VCR, from a broadcast televisionsignal, etc.; the pictures may be static or still or they may be movingpictures, as in a movie or in a cartoon, for example. Conventionaldisplays also may present visual information of the alphanumeric type,such as numbers, letters, words, and/or other symbols (whether in theEnglish language or in another language). Visual information viewed by aperson (or by a machine or detector) usually is in the form of visiblelight. Such visible light is referred to as a light signal or an opticalsignal. The term optical signal with which the invention may be usedincludes visible light, infrared light, and ultraviolet light, thelatter two sometimes being referred to as electromagnetic radiationrather than light. The optical signal may be in the form of a singlelight ray, a light beam made up of a plurality of light rays, a lightsignal such as a logic one or a logic zero signal used in an opticalcomputer, for example, or the above-mentioned alphanumeric or graphicstype display. Thus, as the invention is described herein, it is usefulwith optical signals of various types used for various purposes.Therefore, in the present invention reference to optical signal, lightray, light beam, light signal, visual information, etc., may be usedgenerally equivalently and interchangeably.

[0005] In an exemplary liquid crystal display sometimes referred to asan image source, there usually are a plurality of picture elements,sometimes referred to as pixels or pels, and these pixels can beselectively operated to produce a visual output in the form of apicture, alphanumeric information, etc. Various techniques are used toprovide signals to the pixels. One technique is to use a commonelectrode on one plate of a liquid crystal cell which forms the displayand an active matrix electrode array, such as that formed by thin filmtransistors (TFT), on the other plate of the liquid crystal cell.Various techniques are used to provide electrical signals to the TFTarray to cause a particular type of optical output from respectivepixels. Another technique to provide signals to the pixels is to use twoarrays of crossed electrodes on respective substrates of an LCD; byapplying or not applying a voltage or electric field between a pair ofcrossed electrodes, a particular optical output can be obtained.

[0006] One factor in determining resolution of a liquid crystal displayis the number of pixels per unit area of the liquid crystal display. Forexample, Sony Corporation recently announced a 1.35 inch diagonal highresolution liquid crystal display which has 513,000 pixels arranged in480 rows of 1,068 pixels per row.

[0007] Another factor affecting resolution is the space between adjacentpixels sometimes referred to “as optical dead space”. Such spaceordinarily is not useful to produce an optical signal output. The spaceusually is provided to afford a separation between the adjacent pixelsto avoid electrical communication between them. The space also isprovided to accommodate circuitry, leads, and various electricalcomponents, such as capacitors, resistors, and even transistors or partsof transistors. The proportion of optical dead space to useful space ofpixels that can produce optical output tends to increase as the physicalsize of the image source is decreased, for the space required to conveyelectrical signals, for example, may remain approximately constantalthough the actual size of the useful space of the pixels to produceoptical output can be reduced because of anticipated imagemagnification. However, upon magnification of the image produced by sucha miniature image source both the optical dead space and the usefuloptical space of the pixels are magnified. Thus, resolution tends to bedecreased, especially upon such magnification.

[0008] The picture elements (pixels or pels) may be discrete pixels,blocks or areas where an optical signal can be developed by emission,reflection, transmission, etc. such as the numerous pixels in theminiature image source of Sony Corporation mentioned above. The opticalsignal referred to may mean that light is “on” or provided as an outputfrom the device, or that the pixel has its other condition of notproducing or providing a light output, e.g., “off”; and the opticalsignal also may be various brightnesses of light or shades of gray.Alternatively, the optical output or optical signal produced by a pixelmay be a color or light of a particular color.

[0009] The pixels may be a plurality of blocks or dots arranged in anumber of lines or may be a number of blocks or dots randomly located orgrouped in a pattern on the display or image source (source of theoptical signal). The pixels may be a number of lines or locations alongthe raster lines that are scanned in a CRT type device or the pixels maybe one or a group of phosphor dots or the like at particular locations,such as along a line in a CRT or other device. The optical signalproduced by one or more pixels may be the delivery of light from thatpixel or the non-delivery of light from that pixel, or variousbrightnesses or shades of gray. To obtain operation of a pixel, forexample, the pixel may be energized or not. In some devices energizingthe pixel may cause the pixel to provide a light output, and in otherdevices the non-energizing of the pixel may cause the providing of alight output; and the other energized condition may cause the oppositelight output condition. It also is possible that the nature of the lightoutput may be dependent on the degree of energization of a pixel, suchas by providing the pixel with a relatively low voltage or relativelyhigh voltage to obtain respective optical output signals (on and off oroff and on, respectively).

[0010] For example, in a conventional twisted nematic liquid crystaldisplay device, polarized light is received by a liquid crystal cell,and depending on whether the liquid crystal cell receives or does notreceive a satisfactory voltage input, the plane of polarization of thelight output by the liquid crystal cell will or will not be rotated; anddepending on that rotation (or not) and the relative alignment of anoutput analyzer, light will be transmitted or not. In an optical phaseretardation device that has variable birefringence, such as thosedisclosed in U.S. Pat. Nos. 4,385,806, 4,540,243, and RE.32,521(sometimes referred to as surface mode liquid crystal cells), dependingon the optical phase retardation provided by the liquid crystal cell,plane polarized light may be rotated, and the optical output can bedetermined as a function of the direction of the plane of polarization.In a CRT light emission or not and brightness may be determined byelectrons incident on a phosphor at a pixel. In electroluminescentdisplays and plasma displays light output may be determined byelectrical input at respective areas on pixels.

[0011] The interlacing of raster lines or display lines is a knownpractice used in television and in other types of display systems. Forexample, in NTSC and PAL television type cathode ray tube (CRI) displaysit is known that two interlaced fields of horizontal lines are used toprovide an entire image frame. First one raster or set of lines isscanned to cause one subframe (sometimes referred to as field) to bedisplayed; and then a second raster or set of lines is scanned to causea second subframe (field) to be displayed. The electrical signals usedto scan one line in one subframe and the electrical signals used to scanthe relatively adjacent line of the subsequent subframe may bedifferent, and, therefore, the optical outputs of those lines may bedifferent. The two raster subframes are presented sufficiently fast thatthe eye of an observer usually cannot distinguish between the respectiveimages of the two successive subframes but rather integrates the twosubframes to see a composite image (sometimes referred to as a frame orpicture). The two subframes are created sequentially by “writing” theimage to respective pixels formed by phosphors to which an electron beammay be directed in response to electrical signals which control theelectron beam in on-off and/or intensity manner. After the electron beamhas reached the end of its scanning to create one subframe, e.g., thelast pixel or phosphor dot area of that field, there is a period of timewhile the electron beam is moved or directed to the first pixel of thenext subframe. During that period of time a blanking pulse is providedto prevent electrons from being directed to phosphors or pixels causingundesired light emission. Sometimes various circuits of a television orCRT display are synchronized to the operative timing of the television,CRT, etc. by synchronization with such blanking pulses.

[0012] The density of pixels, e.g., number of pixels per unit area, in aCRT display usually is, in a sense, an analog function depending oncharacteristics of the electron beam, drive and control circuitry forthe beam, phosphor dot layout, shadow mask(s), etc., as is known.Usually a CRT is driven using the interlaced lines forming the subframesmentioned above. In an LCD, though, there is a fixed number of pixelsper line or row; and data, e.g., whether a given pixel in a row is totransmit light or to block light transmission, usually is written to thepixels a row at a time. The data is written to one row, then to thenext, and so on, and there usually is no interlacing of rows or ofsubframes as there is in CRT driving techniques.

[0013] In some LCD's the two subframes mentioned above usually areeffectively averaged together, when driven by a CRT type of interlacedsignal, since there usually is no physical interlacing of LCD pixels toform respective subframes as there are respective scan lines of phosphordots, for example, in a CRT. Rather, the electrical signals for drivingadjacent scan lines of different respective interlaced subframes of aCRT display, both usually are delivered to only a single row of pixelsin an LCD. Each pixel responds to the electrical signal applied theretoto transmit or to block light, for example. Those two sets of electricalsignals are applied to the row of pixels at different times. Therefore,at one time a given row of LCD pixels may present as an optical outputoptical information from one subframe and at a later time presentoptical information from the other subframe.

[0014] Since the optical information presented in one subframe isexpected to be displaced in space from the optical information presentedin the other subframe to obtain the interlacing pattern of a CRTdisplay, careful examination of the optical output from theabove-mentioned LCD will show an amount of “jittering” of the image.This jittering is caused by the pixels of one row periodically beingchanged so the optical output thereof sequentially displays the resultof energization by signals representing one scan line of informationfrom one subframe and then energization by electrical signalsrepresenting the adjacent scan line of information from the nextsubframe.

[0015] This jittering can degrade the displayed image and can makeviewing uncomfortable. Also, the problems, such as viewing discomfortand/or image degrading, caused by jittering tend to increase as theimage is enlarged or magnified, e.g., when the image is created by arelatively miniature image source, such as the SONY display mentionedabove, and is magnified for direct viewing or for projection by aprojector.

[0016] One technique for reducing the jittering is to use relativelyslow liquid crystal display devices. Therefore, the liquid crystaldisplay element or pixel tends to average the electrical signals appliedthereto. A disadvantage to this technique, though, is that imageresolution is reduced because the information representing two scanlines is combined into a single line. Also, a slow acting liquid crystaldisplay element tends to have undesirable hysteresis that slows motionbeing shown by the display.

[0017] In a color display, such as a LCD (liquid crystal display), thereusually are red, green and blue pixels which form a color triad(hereinafter referred to as triad). By operating the LCD in such a waythat one or more of the pixels forming a triad provides (or produces)the respective color light of that pixel, different respective colorsand white can be produced as output light. For example, if the red pixelof a triad were providing red output light; and the green and bluepixels were not providing output light, the light output from that triadwould be red. Further, when two or more pixels of a triad are providinglight output, a combination of those colors is seen by a person viewing(sometimes referred to as the viewer) the light output or image. Theviewer usually visually superimposes the output light from the pixels ofthe triad; and the combined or superimposed lights therefrom provide thenet effect or integrated light output of the triad. As an example, toproduce a white light output from a triad, the red, green and bluepixels of that triad would provide, respectively, red, green and bluelight; and those lights would be, in effect, superimposed by the viewerand seen as white light.

[0018] There is a continuing need and/or desire to improve resolution ofdisplays. It also would be desirable to facilitate the placing ofcircuitry in a display while minimizing the optical dead space caused bythe circuitry. There also is a need to reduce jitter.

[0019] In the above-mentioned patent applications are disclosedtechniques for actively dithering, moving an optical signal, changingthe location or optical path of an optical signal, etc. for severalpurposes, such as to increase resolution, to reduce jitter, and so on.There also are disclosed techniques for passive dithering, moving ofoptical signals, etc., for example to increase the fill factor of animage provided by a display by expanding the image or pixels forming theimage.

[0020] An LCD using the twisted nematic effect usually cannot switchbetween transmission states as rapidly as changes occur in the appliedelectrical signal which operates the LCD. For example, the electricalinput to a twisted nematic LCD can change nearly instantly, but it takesa number of milliseconds for the LCD to respond dynamically to thechange in electrical input to change the optical response of the LCD.When an LCD is used in a display system that employs dithering todouble, quadruple or otherwise to change the effective number of pixels,for convenience hereinafter, sometimes referred to as optical linedoubling (or OLD), the relatively slow response of the twisted nematicLCD compared to the faster operation of the dithering optics can resultin an optical output that does not achieve the desired improvement inresolution or other optical effect.

[0021] The displaying of a dark scene using a display device (sometimesreferred to as a passive display), which modulates light received from aseparate light source, encounters a disadvantage which ordinarily is notpresent for displays which produce their own light, such as a cathoderay tube (CRT). The problem has to do with reduced resolution and/orcontrast of the displayed image.

[0022] In a CRT, for example, when it is desired to display a darkscene, the intensity of the output light can be reduced. The differentparts of the dark scene, then, all may be output at the reducedbrightness or illuminance level. All pixels (e.g., picture elements,phosphor dots in a monochrome display or group of three red, green andblue phosphor dots for a multicolor display, etc.) of the CRT can beactive so that resolution is maintained even though intensity of thelight produced by the phosphors is reduced.

[0023] However, in a passive display device, such as a liquid crystaldisplay, an electrochromic display, etc., whether of the lighttransmitting type or of the light reflecting type, the usual practice toreduce brightness of a displayed image or scene is to reduce the numberof pixels which are transmitting light at a particular moment. Such areduction reduces the resolution of the display. Also, such a reductioncan reduce the contrast of the display.

[0024] The human eye has difficulty distinguishing between seeing orrecognizing the difference between low and high brightness and contrastranges. This difficulty is increased when the number of pixels isdecreased and resolution is degraded.

[0025] It would be desirable to improve the contrast and resolution ofpassive displays.

[0026] In U.S. patent application Ser. No. 08/187,163 is disclosed apassive apparatus, such as an LCD, and method for displaying images withhigh contrast by controlling the light input to the display to controlbrightness of the output while operating respective pixels of thedisplay to obtain good contrast substantially without regard to theoutput brightness. Different color effects also are disclosed using, forexample, field sequential switching of respective color light. However,this is another example of a passive optical device, in this case anLCD, in which field sequential switching could be improved ifcoordinated with the delays inherent in the dynamic optical response ofa liquid crystal cell, for example, relative to the changes in operatingsignal, such as electric field, voltage, etc.

[0027] As is described in application Ser. No. 08/187,163, an image of acandlelit room would be dim. In the prior art devices a relatively smallnumber of pixels would be used, then, to transmit light to create theimage, whereas a relatively large number of pixels would be used toblock light transmission to give the effect of the reduced intensity ordim room. In the invention of such application, though, the number ofpixels used to create the image remains constant, and the contrast ratiobetween one portion and another portion of the image remain constant;only the intensity of the illuminating light changes thereby to diminishthe brightness of the room. Therefore, with the invention image data isnot lost regardless of the brightness of the image, whereas in the priorart image data is lost because the additional pixels are used tobrighten or darken the brightness of the image.

[0028] The features of the invention as described in that patentapplication can be used in a frame sequential basis. The features of theinvention can be used regardless of whether the display is operated inreflective mode or in transmissive mode. Also, the features of theinvention can be used in a virtual reality type display in order toprovide a very wide range of contrast and of image brightnesscharacteristics. The picture information is used to derive thebrightness of the display, not the surrounding ambient. Using theinvention of that application, the amount of information that can beconveyed by the display is substantially increased over the prior art.

[0029] For example, if there were a grey scale of 100 shades of grey anda display with 10 shades of grey, the intensity of the illuminatingsource can be changed at 10 different levels, for example, and therealso can be 10 different shades of grey provided by the display itself.Therefore, this provides 100 shades of grey. This characteristic can beincreased by another factor of 10 by going to r, g, b (red, green, blue)modulation on a field sequential basis, which allows the possibility of10 to the 6th different illumination levels and colors. The foregoing isespecially important in head mounted displays where immersion in theimage is extremely important. Using features of such patent application,there can be high illumination of the scene, then, the grey scalecontrast ratio of the real image can be adjusted. As a result, there isa high contrast image presented in a bright motif. Another example usingsuch invention is the ability to display a sunrise scene in which thered image is enhanced and the blue and green are minimized.

[0030] The invention of that application, then, can separate the twofunctions of brightness and image. The image is a function of theoperation of the liquid crystal modulator and the illuminationbrightness is the function of the light source intensity. The r, g, bcolors can be changed to give a candlelight or moonlight effect withgood resolution and color function, but the brightness of the scene is afunction of the background. As a result, it is possible to photographthe scene in daylight to get good contrast; and then by reducing thedisplay illumination it is possible to give the impression of a moonlitor candlelit environment.

SUMMARY

[0031] With the foregoing in mind, then, one aspect of the invention isto increase the resolution of a display by electro-optically ditheringan optical signal.

[0032] Another aspect relates to use of electro-optical dithering toobtain three dimensional images, especially using auto-stereoscopiceffect.

[0033] Another aspect relates to using electro-optical dithering toeffect beam switching of optical signals.

[0034] Another aspect is electro-optically to change selectively thelocation at which an optical output signal is presented to anotherlocation. A further aspect is to effect such change in more than onedirection, e.g., along more then one axis.

[0035] According to another aspect, a device for changing or determiningthe location of an optical signal includes birefringent means forselectively refracting light based on optical polarizationcharacteristic of the light, and means for changing such opticalpolarization characteristic of light, the birefringent means and thechanging means being cooperative selectively to change the location ofthe optical signal.

[0036] According to another aspect, a system for increasing theresolution of an optical display having a plurality of picture elementsincludes birefringent means for selectively refracting light based onpolarization characteristics of the light, changing means forselectively changing the polarization characteristics of light, and thebirefringent means and the changing means being in optical series andcooperative in response to selective operation of the changing means tochange the location of output optical signals therefrom.

[0037] According to another aspect, a display system includes a displayfor producing visual output information by selective operation of aplurality of picture elements at respective locations, and means forchanging the location of the output information as a function of opticalpolarization thereby effectively to increase the number of pictureelements.

[0038] According to another aspect, a display system includes a displayfor producing visual output information by selective operation of aplurality of picture elements at respective locations, and means forchanging the location of the output information without physicalrealignment of a mechanical device thereby effectively to increase thenumber of picture elements.

[0039] According to another aspect, a display system includes a displayfor producing visual output information by selective operation of aplurality of picture elements at respective locations, and means forelectro-optically changing the location of the output informationthereby effectively to increase the number of picture elements.

[0040] According to another aspect, a method for displaying visualinformation includes presenting a first optical output from a source byproviding plural optical signals arranged in a pattern, presenting asecond optical output from the source by providing plural opticalsignals arranged in a pattern, and selectively shifting the location ofthe pattern of the second optical output relative to the location of thepattern of the first optical output based on optical polarization.

[0041] According to another aspect, an electro-optical dithering systemfor shifting polarized light includes birefringent means for selectivelyrefracting light as a function of a polarization characteristic of thelight, and changing means for changing the polarization characteristicof polarized light to provide output light that is shifted or not as afunction of optical polarization.

[0042] According to another aspect, a method of making a displayincludes positioning in optical series an image source, a birefringentmeans for selectively refracting light based on optical polarizationcharacteristic of the light, and a changing means for changing suchoptical polarization characteristic.

[0043] Using principles of the invention, the location of an opticalsignal can be changed, and the change can be used for a number ofpurposes. For example, the change can be used to improve resolution of adisplay, to provide an auto-stereoscopic output, to interlace opticalsignals, to facilitate positioning and hiding of circuitry used in adisplay, to facilitate overlapping of tiles or pixels in a display, etc.A number of these examples are presented below. The invention may beused to achieve one or more of those and other uses.

[0044] An aspect of the invention relates to an optical line increaser,wherein the number of pixels in a optical display can be increased byelectro-optical means.

[0045] An aspect of the invention relates to an optical line increaser,wherein the number of pixels in a optical display can be increased byelectro-optical means, for example, to double, triple, quadruple, orotherwise to increase the effective number of pixels presenting outputoptical information for viewing by a person, machine, other device,etc., and/or for other use.

[0046] Another aspect is to hide or to reduce optical dead space in adisplay.

[0047] Another aspect is to use a switchable electro-optical device toeffect dithering (changing effective location) of an optical signal.

[0048] Another aspect is to reduce jitter in an optical display.

[0049] Another aspect is to drive a non-interlaced display using aninterlaced signal and electro-optically dithering the optical output ofthe display to reduce jitter.

[0050] Another aspect is to increase the effective number of pixelsand/or lines of an optical display.

[0051] In accordance with a further aspect of the invention, a passivedithering display system includes an optical display including aplurality of pixels with optical dead space between the pixels forproducing an image, and a birefringent material for shifting onepolarization component of the image relative to a second polarizationcomponent of the image such that the shifted polarization component liesin the dead space.

[0052] In accordance with another aspect, a display system includes anoptical display for producing an image and a first birefringent materialfor refracting one component of the image relative to a second componentof the image based on polarization characteristics of the components toproduce a plurality of adjacent images.

[0053] In accordance with a still further aspect of the invention, amethod of reducing optical background noise includes the steps ofdisplaying a plurality of pixels with optical dead space between saidpixels for producing an image and shifting one polarization component ofthe image relative to a second polarization component of the image suchthat the shifted polarization component lies in the dead space.

[0054] Another aspect relates to expanding an image or pixels of animage to increase the fill factor of the image, the fill factor relatingto the amount of area of the image actually occupied by image comparedto that part of the image occupied by optical dead space.

[0055] Another aspect relates to using passive image or pixel expandingto increase the fill factor of an image.

[0056] Another aspect relates to using active image or pixel doubling(or other increasing) to increase fill factor and resolution of animage.

[0057] Another aspect relates to techniques to superimpose color pixelimage light outputs to obtain respective color outputs for a display.

[0058] Another aspect is to increase the amount of data able to bedisplayed from a video signal or the like provided to a display system,such as an LCD display system or other display system.

[0059] As is described further below, the invention is useful tocoordinate light output by an optical device, such as an LCD, forexample, and the dynamic operation of such optical device with anotheroptical device, such as one that switches or shifts the location of theoutput light for use, such as viewing, projection, etc., one thatdisplays images in field (sometimes referred to as frame or part of aframe) sequential operation to present images with good contrast and/orcolor effect that are independent of the brightness of the output light,and so on.

[0060] One or more of these and other objects, features and advantagesof the present invention are accomplished using the invention describedand claimed below.

[0061] To the accomplishment of the foregoing and related ends, theinvention, then, compresses the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrativeembodiments of the invention. These embodiments are indicative, however,of but a few of the various ways in which the principles of theinvention may be employed.

[0062] Although the invention is shown and described with respect tocertain preferred embodiments, it is obvious that equivalents andmodifications will occur to others skilled in the art upon the readingand understanding of the specification. The present invention includesall such equivalents and modifications, and is limited only by the scopeof the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In the annexed drawings:

[0064]FIG. 1 is a schematic side elevation view of a CRT displayincluding an electro-optical dithering system according to the presentinvention;

[0065]FIG. 2 is a schematic illustration of the components of theelectro-optical dithering system of FIG. 1;

[0066]FIG. 3 is a schematic illustration of the double refraction effectthrough a calcite crystal which may be used in the electro-opticaldithering system of the invention;

[0067]FIGS. 4A, 4B and 4C are, respectively, schematic illustrationsindicating exemplary axial alignment of the several components of theelectro-optical dithering system shown in FIG. 2;

[0068]FIGS. 5A, 5B and 5C are, respectively, schematic illustrationssimilar to FIG. 2 showing the operation of the electro-optical ditheringsystem on light in respective operational modes;

[0069]FIG. 6 is a schematic illustration of an alternate embodiment ofelectro-optical dithering system;

[0070]FIG. 7 is a schematic front view of the face or display output ofa CRT showing exemplary raster lines;

[0071]FIG. 8 is a schematic side elevation view of the electro-opticaldithering system of the invention used in an auto-stereoscopic display;

[0072]FIG. 9 is an enlarged view of a single lens element of theauto-stereoscopic display of FIG. 8;

[0073]FIG. 10 is a schematic plan view of part of a liquid crystaldisplay showing areas where pixels are located and areas where there iscircuitry or dead space located between adjacent pixels and includingthe electro-optical dithering system of the invention;

[0074]FIG. 11 is a schematic top view of the display of FIG. 10 showingthe paths of optical signals that are shifted in location according tothe on or off state of the electro-optical dithering system of thedisplay;

[0075]FIGS. 12 and 13 are schematic block diagrams of synchronizingcircuit techniques useful in the various display systems of theinvention;

[0076]FIGS. 14 and 15A-15E are schematic illustrations of a displaysystem and parts thereof with a double electrooptical dithering system;

[0077] FIGS. 16A-16D are schematic illustrations of a pixel pattern thatis dithered or not in up to four different spatial pattern locations;

[0078]FIG. 17 is a composite of the pixel patterns of FIGS. 16A-16D;

[0079]FIGS. 18 and 19 are schematic illustrations of a display systemwith a double electrooptical dithering system and parts thereof usingswitchable liquid crystal birefringent devices;

[0080]FIG. 20 is a schematic illustration of part of a red, green andblue pixel arrangement for a multicolor display;

[0081]FIG. 21 is a schematic illustration of a segmented display systemwith selective time sequenced dithering of respective segments;

[0082] FIGS. 22A-22F are schematic illustrations of the segmenteddisplay system of FIG. 21 showing the time sequence of operationthereof;

[0083]FIG. 23 is a schematic illustration of a passive dithering systemused in connection with a display which produces a polarized output;

[0084]FIG. 24 is a schematic illustration of the effect of dithering inboth horizontal and vertical directions;

[0085]FIG. 25 is a schematic illustration of the orientations of theoptic axes of the components of the passive dithering system of FIG. 23;

[0086]FIG. 26 is a schematic illustration of the passive ditheringsystem of FIG. 23 used in connection with a display which produces anonpolarized (sometimes referred to as unpolarized) light output;

[0087]FIG. 27 is a schematic illustration of the orientations of theoptic axes of the components of the passive dithering system of FIG. 26;

[0088]FIG. 28 is a schematic illustration of an alternate embodiment ofa passive dithering system;

[0089]FIG. 29 is a schematic illustration of the orientations of theoptic axes of the components of the passive dithering system of FIG. 28;

[0090]FIG. 30 is a schematic illustration of the passive ditheringsystem of FIG. 28 used in connection with a display which produces anonpolarized light output;

[0091]FIG. 31 is a schematic illustration of an optical display systemusing an alternate embodiment of a passive dithering system usingunpolarized light input;

[0092]FIG. 32 is a schematic illustration of the orientations of theoptic axes of the components of the passive dithering system of FIG. 31;

[0093]FIG. 33 is a schematic illustration of an alternate embodiment ofoptical display system using an active dithering system for diagonallydisplacing a pixel image;

[0094]FIG. 34 is a schematic illustration of the locations of theoriginal pixel images unshifted and of the shifted pixel images usingthe dithering system of FIG. 33;

[0095]FIG. 35 is a schematic illustration of an alternate embodiment ofoptical display system using active and passive dithering system fordisplacing pixel images;

[0096]FIG. 36 is a schematic illustration of the locations of theoriginal pixel images unshifted and of the shifted pixel images usingthe dithering system of FIG. 35 in four respective operations;

[0097]FIG. 37 is a schematic illustration of the display output from anoptical display system of the type shown in FIG. 35, for example,showing shifting of pixel images relative to each other to obtainsuperpositioning of color pixel images and increased fill factor;

[0098]FIGS. 38 and 39 are schematic illustrations of display outputsfrom an optical display system of the type shown in FIG. 35 and or inother figures hereof, for example, showing shifting of pixel images intogaps between pixels and in overlapping relative to each other;

[0099]FIG. 40 is a schematic illustration of the display output from anoptical display system of the type shown in FIG. 41, for example,showing shifting of pixel images according to an exemplary prescribedpattern;

[0100]FIG. 41 is a schematic illustration of an optical display systemincluding the components to obtain the operation depicted in FIG. 40 fora head mounted or boom mounted display system or other display system;

[0101]FIG. 42 is a schematic illustration of a display system inaccordance with an embodiment of the invention including a head mountedportion;

[0102]FIG. 43 is a schematic section elevation view showing the variousoperational parts of the monocular viewing device used in the displaysystem of FIG. 1;

[0103]FIG. 44 is a compilation of graphs representing the response of atwisted nematic LCD display pixel when addressed at 60 Hz (Hertz);

[0104]FIG. 45 is a compilation of graphs representing the response of atwisted nematic LCD display pixel when addressed at 120 Hz;

[0105]FIG. 46 is a compilation of graphs representing the response of asurface mode type birefringent liquid crystal light shutter operating asan optical rotator or switch coordinated with the operation of a twistednematic LCD display pixel which is addressed at 120 Hz;

[0106]FIG. 47 is a schematic illustration of a display optical systemused in the viewing device of FIGS. 42-43, for example, and/or in otherviewing devices or display systems disclosed herein;

[0107]FIG. 48 is a compilation of graphs showing the relationship oftiming signals for an optical line doubler system that provides bothhorizontal and vertical doubling (e.g., quadrupling of respectivepixels), for example, as in the embodiment depicted in FIGS. 14-17;

[0108]FIG. 49 is a schematic illustration of a light transmissivedisplay system according to an embodiment of the invention;

[0109]FIG. 50 is a schematic illustration of a light reflective displaysystem according to an embodiment of the invention;

[0110]FIG. 51 is a schematic view of a reflective field sequentialdisplay and illumination system using plural cholesteric liquid crystalreflectors and plural light sources of respective colors to provide amulticolor or full color display useful in various embodiments of theinvention;

[0111]FIG. 52 is a schematic view of a head mounted display systemincluding a pair of display subsystems in accordance with variousembodiments of the invention; and

[0112] FIGS. 53-58 are schematic graphical illustrations depictingoperation of the invention;

[0113]FIG. 59 is a schematic illustration of a delta arrangement ofpixels forming respective triads of a color display, such as a liquidcrystal display (LCD);

[0114]FIG. 60 is a schematic illustration of a line arrangement ofpixels forming respective triads of a color display, such as an LCD;

[0115]FIG. 61 is a schematic illustration of a display system, includinga display and an optical shifting system, in accordance with anembodiment of the invention, especially in conjunction with theillustrations of FIGS. 59, 60, and the following FIGS. 62-65;

[0116]FIG. 62 is a schematic illustration showing shifting of respectivepixels in one row to locations in another row to increase pixel density;

[0117]FIG. 63 is a graphical timing diagram depicting operation of thedisplay system of FIG. 61, for example, carrying out functions depictedin FIGS. 59 and 62 to increase pixel density;

[0118]FIG. 64 is an enhanced graphical timing diagram similar to that ofFIG. 63, depicting operation of the display system of FIG. 61, forexample, carrying out functions depicted in FIGS. 59 and 62 to increasepixel density; and

[0119]FIG. 65 is another enhanced graphical timing diagram similar tothat of FIG. 64, but including a phase shift.

DESCRIPTION

[0120] Referring, now in detail to the drawings wherein like referencenumerals designate like parts in the several figures and initially toFIG. 1, an electro-optical dithering system in accordance with anembodiment of the present invention is generally indicated at 1 in usewith a display 2 to form an optical display system 3 for providingoptical signals, visual information, etc., as the output therefrom. Thedisplay 2 provides a source of light or optical signals, and such lightis transmitted through the electro-optical dithering system to provideoptical signals at respective locations for viewing or the like.Exemplary light is represented by an arrow 4, such as an optical signalproduced at a particular location by the display 2 or produced by someother source and modulated by the display 2 as the output therefrom.

[0121] The location of the output optical signal 5 is represented byarrows 5 a, 5 b. Those arrows 5 a, 5 b represent the location of theoutput optical signal 5 resulting from the optical signal 4 beingtransmitted through the electro-optical dithering system 1 while theelectro-optical dithering system is in a respective one or the other ofthe operative states thereof, such as off or on.

[0122] In the embodiment illustrated in FIG. 1 the display 2 is a CRT.It will be appreciated that the display 2 may be an LCD or anotherdisplay, such as an electroluminescent display, plasma display, flatpanel display or other display.

[0123] Dithering may refer to the physical displacement of an image. Anelectro-optical dithering system (EDS) refers to an electro-opticalmeans to physically shift, translate or to change the location of anoptical signal, such as an image. The image may be shifted along an axisfrom one location to another and then back to the first, e.g. up andthen down, left and then right, etc. The optical signal may be moved inanother direction along a straight or other axis or not along an axis atall. The dithering may be repetitive or periodic or it may beasynchronous in moving an image from one location to another and thenholding it there, at least for a set or non-predetermined time.

[0124] The electro-optical dithering system 1, as it is shown in FIG. 1,includes birefringent material, which sometimes is referred to as doublerefracting material, 10. An example of birefringent material is acalcite crystal material. Other double refracting (birefringent)materials also may be used. Birefringent material may transmit lightstraight through or may refract the light which is incident thereon,depending on a characteristic of the light incident thereon, such asoptical polarization characteristic. In the illustrated embodiment theoptical polarization characteristic is the direction of the electricvector of plane polarized light. Plane polarized light having onedirection of electric vector (sometimes referred to as direction of thepolarization axis, the transmission axis of the polarizer or of thelight, the plane of polarization of the light, the direction ofpolarization, etc.) may transmit directly through the birefringentmaterial 10 without being refracted or bent, whereas light having adifferent direction of plane of polarization may be refracted (bent) bythe birefringent material 10. For example, plane polarized light whichencounters one index of refraction characteristic, such as an ordinaryindex of refraction characteristic, of the birefringent material may betransmitted without refraction. However, plane polarized light whichencounters a different index of refraction characteristic, such as theextraordinary index of refraction, of the birefringent material willbend or refract at the interface with the birefringent material, bothupon entering and upon leaving the birefringent material. Therefore, ina sense the birefringent material 10 changes the direction of lighttransmitted through it, for example, as it changes the location of theoutput optical signal from location 5 a to 5 b.

[0125] In the optical display system 3 embodiment illustrated in FIG. 1the electro-optical dithering system 1 also includes a switch 11 thatcan be operated to change the characteristic of light relevant to thebirefringent material 10 to change the location of the output opticalsignal. In the exemplary embodiment of FIG. 1 refraction of light ortransmission of light without refraction by the birefringent material 10depends on the direction of polarization of plane polarized lightincident on the birefringent material 10, and the switch 11 is able toswitch the direction of polarization of such light incident on thebirefringent material 10.

[0126] In the embodiment illustrated in FIG. 1 the switch 11 is a liquidcrystal cell or liquid crystal shutter type device which is able totransmit light to the birefringent material 10 such that the lightincident on the birefringent material has a plane of polarization thatcan be changed by the switch. Accordingly, if the switch is in oneoperative state or mode, the light incident on the birefringent material10 may have a plane of polarization such that the output optical signal5 occurs at the location of the arrow 5 a, and with the switch 11 in adifferent state of energization the plane of polarization of the lightincident on the birefringent material 10 can be changed (e.g., switchedto an orthogonal direction to the first-mentioned plane) thereby tocause the output optical signal to occur at the location of the arrow 5b.

[0127] A linear polarizer (sometimes referred to as a plane polarizer)12 is between the switch 11 and the CRT display 2. The light 4 providedby the display 2 is plane polarized by the polarizer 12. The directionof polarization in cooperation with one condition of the switch 11 willresult in the light being transmitted directly through the birefringentmaterial 10 without refraction so as to appear at location of arrow 5 a.However, in response to the other condition of the switch 11, the lightwill be refracted by the birefringent material 10 so as to occur at thelocation of the arrow 5 b.

[0128] With the foregoing in mind, then, it will be appreciated that theinvention includes a material that can move the location of an outputoptical signal relative to the location of an incident (input) opticalsignal depending on a characteristic of the incident optical signal,such as the direction of plane polarized light. The electro-opticaldithering system 1 of the invention includes birefringent, doublerefracting, or equivalent material and a means to switch or todiscriminate the characteristic of the incident optical signal.

[0129] In the embodiment illustrated in FIG. 1, the light 4 from a CRTis unpolarized. The polarizer 12 gives the light a characteristic oflinear (plane) polarization. The switch 11 can change the direction ofpolarization, e.g., the direction of the electric vector of thepolarized light. The birefringent material provides the output opticalsignal at the location 5 a, 5 b, depending on the characteristic of thelight incident on the birefringent material.

[0130] The switch 11 may be a liquid crystal cell or several liquidcrystal cells, such as twisted nematic liquid crystal cells,birefringent liquid crystal cells, such as those disclosed in U.S. Pat.Nos. 4,385,806, RE.32,521, and 4,540,243, the entire disclosures ofwhich hereby are incorporated by reference. If desired, the liquidcrystal cells may be arranged in optical series and operated as apush-pull arrangement to improve linearity of response, and/or for otherpurposes, for example, as is disclosed in one or more of theaforementioned patents. Other types of liquid crystal cells also may beused for the switch 11. Further, other types of devices that are able toswitch the optical characteristic of light, such as the direction ofplane polarization, etc., may be used for the switch 11; severalexamples include ferro-electric liquid crystal cells, variable opticalretarders, PLZT devices, and so on.

[0131] An advantage to using a liquid crystal display (LCD) as thedisplay 2 with the dithering system 1 is that the output light from anLCD usually already may have a characteristic of optical polarization,such as linear polarization. In such a case, the linear polarizationcharacteristic provided by such displays may eliminate the need for aseparate linear polarizer 12.

[0132] In FIG. 2 the electro-optical dithering system 1 is shown in usein an optical display system 13 having a transmissive LCD 20. The LCD 20may be a twisted nematic liquid crystal display, birefringent liquidcrystal display, or some other type of liquid crystal display whichproduces in response to input light 21 from a light source 22, outputlight represented by an arrow 23. The LCD 20 may be transmissive orreflective. The output light 23 may be, for example, a graphic image,one or more light beams that are selectively turned on or off dependingon operation of the liquid crystal display 20, etc. The graphic imagemay be a moving image, an alphanumeric display, etc. The ditheringsystem 1 includes a birefringent material 10 and a switch 11. Tosimplify the following description, the switch 11 may be referred to asa polarization rotator, which rotates the plane of polarization of thelight represented by arrow 23 an amount depending upon the energizationstate or condition of the polarization rotator. For example, if theswitch 11 were a twisted nematic liquid crystal cell, when it isde-energized, it would rotate the plane of polarization by 90degrees (orsome other amount depending on the nature of the liquid crystal cell),and when the twisted nematic liquid crystal cell is in a fully energizedcondition, it would not rotate the plane of polarization of the lightincident thereon. Similar operation could be obtained by usingbirefringent liquid crystal cells. Additionally, if desired,compensation may be provided for residual retardation in a liquidcrystal cell, whether of the birefringent or twisted nematic type; suchcompensation may be provided by a wave plate or the like, such as aquarter wave plate positioned in a particular orientation relative tothe rub direction or axis of the liquid crystal cell used in the switch11.

[0133] Further, a wave plate, such as a half wave plate, may be used torotate the plane of polarization of light 23 so it is appropriatelyaligned with the optic axis (sometimes referred to herein as the rubdirection, optical axis, or simply axis) of the switch 11. For example,if the switch 11 were a twisted nematic liquid crystal cell, the planeof polarization of the light 23 may be parallel or perpendicular to therub direction of one of the plates of the liquid crystal cell. If theswitch 11 were a birefringent liquid crystal cell, such as a surfacemode cell or a pi-cell (e.g., as the above-mentioned patents or in U.S.Pat. No. 4,582,396, which is hereby incorporated by reference), theplane of polarization of light 23 may be at 45 degrees to the rubdirection. In using a half wave plate to adjust plane of polarization,for example, the axis of the half wave plate would be aligned to onehalf the angular distance between the orientation of the plane ofpolarization of the light incident on the half wave plate and theangular orientation desired for the light output from the half waveplate.

[0134] Turning to FIG. 3, there is shown an example of birefringentmaterial 10 in the form of the mineral calcite, also referred to as acalcite crystal 30. Unpolarized light 31 enters the calcite 30 at theleft hand face 32 thereof. The light enters at a right angle to the face32. The light 31 is resolved into two orthogonally polarized components33, 34 in view of the birefringent nature of the calcite. The opticalaxis of the light components 33, 34 are oriented such that one component33 has a plane of polarization or electric vector direction into and outof the plane of the drawing of FIG. 3, as is represented by the dotsshown in FIG. 3, and such light 33 experiences an index of refractionchange between the environment 35 outside the calcite 30 and theenvironment 36 inside the calcite 30. However, the axis of the calcitecrystal 30 is at a right angle to the plane of polarization to the light33, and, therefore, this components of light 33 travels through thecalcite crystal 30 without deflection (refraction); sometimes this lightis referred to herein as the undithered light.

[0135] The light component 34 is polarized vertically in the plane ofthe drawing of FIG. 3 and is represented by a double-headed arrow in thedrawing. The light component 34 experiences a change in index ofrefraction as above; however, the light component 34 also encounters thecalcite crystal axis at an angle which is other than a right angle.Therefore, the light component 34 is refracted and its path is deflected(direction is changed) as it enters and leaves the crystal on its travelthrough the crystal 30, as is shown in FIG. 3; sometimes this light isreferred to herein as the dithered light. This property of refraction ofone polarization component and no refraction of the other polarizationcomponent of light incident on a birefringent material sometimes iscalled double refraction, and it occurs in many materials. The amount ofphysical displacement between the light components 33, 34 where theyexit the right hand face 37 of the calcite crystal 30 and become,respectively, output light 33 a, 34 a represented by arrows at locations38 a, 38 b, respectively, depends on the thickness of the calcitecrystal, indices of refraction of the calcite crystal and the externalenvironment thereof, and the orientation of the optical axis of thespecific material, as is known.

[0136] In the optical display system 3 of FIG. 1 in which the display 2is a CRT and in the optical display system 13 of FIG. 2 which uses anLCD 20 the direction of polarization of light incident on the switch 11and the orientation of the switch 11 may be related for optimaloperation. In one example of the invention, the switch 11 is abirefringent liquid crystal cell (or a pair of them operating inpush-pull manner), and such liquid crystal cell(s) has (have) an axiswhich sometimes is referred to as the rub direction, alignmentdirection, optic or optical axis, etc. of the liquid crystal cell. Usingsuch a liquid crystal cell in the systems 3 or 13, for optimal operationthe polarization direction (transmission direction axis of the polarizer12 or of the LCD 20, for example) should be at 45 degrees relative tothe axis of the switch 11. Additionally, preferably the projection ofthe axis of the calcite crystal 30 is oriented at 45 degrees to the axisof the switch 11. These relationships are depicted in FIGS. 4A, 4B and4C.

[0137] Briefly referring to FIGS. 4A, 4B and 4C, the above-describedrelationships of axes is shown. In FIG. 4A the transmission axis of thepolarizer 12 or the plane of polarization of light delivered by theliquid crystal display 20 or by CRT 2 and polarizer 12 is shown ashorizontal at 40. However, such direction also may be vertical, becauseit is desired that the relationship between that axis and the axis ofthe liquid crystal cell(s) of the birefringent liquid crystal cellswitch 11 be at a relative 45 degrees thereto. Such 45 degreesrelationship is shown by the respective axes 41, 42 for the switch 11.In fact, such axes 41, 42 may represent the axis of one liquid crystalcell and the axis of a second liquid crystal cell, the two beingarranged in optical series and being operated in push-pull fashion. Theaxes 43, 44 of the calcite crystal 30 are shown as horizontal andvertical. However, the vertical axis actually is tipped in or out of theplane of the drawing and it actually is the projection of that axeswhich would appear as vertical; alternatively or additionally thehorizontal axis may be tipped. Such projection of the axes preferably isat 45 degrees to the axes 41, 42 of the switch 11. The describedrelative orientation of the axes of the various components used inconnection with the invention is exemplary, and it will be appreciatedthat other arrangements may be used to obtain a particular type ofoperation. However, in the ideal simplified case described herein, therelationship described may be employed. Also, it will be appreciatedthat compensation may be provided to adjust the effective orientation ofa particular axis. Such compensation can be provided using abirefringent material, a wave plate, such as a quarter wave plate oranother one, etc., as was mentioned above.

[0138] It will be appreciated that whether the axis of a birefringentswitch 11 is at plus or minus 45 degrees, represented by the axis lines41, 42, for example, and whether a respective axis 43, 44 of the calcite30 or other double refracting material 10 is at plus or minus 45 degreesto the axis of the birefringent switch (and parallel or perpendicular tothe plane of polarization 40) will determine whether the ditheredoptical signal will be moved up, down, left or right relative to theundithered signal. If the switch 11 were a twisted nematic liquidcrystal cell, the axis 40 may be parallel or perpendicular to one of theaxes of the liquid crystal cell, and the orientation of the calcite 30may be as shown in FIG. 4C relative to the plane of polarization of thelight represented at 40 in FIG. 4A.

[0139] It will be appreciated that the arrangement of axes hereindescribed are exemplary. The alignment of the switch 11, whatever thatcomponent is comprised of, preferably is such that the switch is able tochange a characteristic of light in the display system 3, 13 (and othersdescribed herein, for example) so that selective dithering can becarried out by a double refraction or other functionally equivalentmaterial or device. Orientation of the double refracting material may besuch as to cause such selective dithering depending on an opticalcharacteristic of the light, which is incident thereon and/or istransmitted therethrough, relative to the double refracting material.

[0140] Quarter wave plates, other wave plates, etc. may be used inconjunction with coupling of light along optical paths used in theelectro-optical dithering system 1 and/or the optical display systems 3or 13, etc. Also, such wave plates may be used to convert planepolarized light to circularly polarize light or vice versa, depending onthe nature of the optical coupling occurring in the various componentsand optical paths and/or the switch 11 used in the invention.

[0141] Referring to FIGS. 5A, 5B and 5C, operation of the EDS 1according to the invention is depicted for use in the exemplary systems3, 13, etc., which are expressly described herein, and in other displaysystems, too. Light 4, for example, from a CRT, is horizontallypolarized by the polarizer 12. Arrow 50 represents such horizontalpolarization, as does the dot in that arrow 50. The switch 11 is abirefringent liquid crystal cell of the type disclosed in theabove-mentioned patents (such types sometimes being referred to as“surface mode” or “pi-cell” liquid crystal devices). When the switch 11is in the high voltage state it does not affect the state ofpolarization of the light 50. Therefore, light 51 exiting the switch 11also has horizontal polarization, e.g., into and out of the plane of thepaper of the drawing. The light 51 enters the double refracting material(birefringent material) 10 and is transmitted without any deflection andis provided as output light 52 at the location and in the direction ofarrow 5 a.

[0142] Referring to FIG. 5B, when the switch 11 is in the low voltagestate, it rotates the plane of polarization of the light 50 preferably90 degrees, i.e., into the vertical plane, as is shown by the verticalarrow 53 associated with the light 51. The vertically polarized lightenters the double refracting material 10 and its path is physicallydisplaced, as is represented by dashed line 54 resulting in output light52 at the location and in the direction of the arrow 5 b.

[0143] Briefly referring to FIG. 5C, the electro-optical ditheringsystem 1 is shown having the light output 52 selectively switchedbetween the location of the arrows 5 a when the switch 11 is in the highvoltage (no rotation of plane of polarization) state and the location ofthe arrow 5 b, which occurs when the switch 11 is in the low voltage(polarization rotating) state. The light represented by arrow 5 a ishorizontally polarized, and the light represented by the arrow 5 b isvertically polarized, as is represented in the drawing of FIG. 5C. Byselectively energizing and de-energizing or, in any event, operating theswitch 11 between two mentioned voltage states, which switch thepolarization characteristic of the light, the location of the outputoptical signal 52 can be switched between the locations represented byarrows 5 a and 5 b.

[0144] A modified optical display system 60 is shown in FIG. 6 using anelectro-optical dithering system 1, as was described above, incombination with an output polarizer (analyzer) 12′. The analyzer 12′may be a linear (plane) polarizer or some other device which candiscriminate between the characteristics of light incident therein, suchas the direction of plane of polarization, circular polarization, etc.The parts of the electro-optical dithering system 1 include abirefringent material 10, such as a calcite material described above,and a switch 11, such as one of the liquid crystal cell devicesdescribed above, or some other device, as will be appreciated.

[0145] The incident light 4 is received from a light source or imagesource, such as a CRT 2 or some other device that delivers unpolarizedlight output. Such unpolarized light 4 incident on the birefringentmaterial 10 is divided into two components 61, 62. The light component61 is horizontally polarized and it is transmitted directly through thebirefringent material 10 without deflection or refraction. The lightcomponent 62 is polarized in the vertical direction, and it is refractedso that its direction is changed (path is deflected) in the manner shownrepresentatively in FIG. 6.

[0146] It will be appreciated that here and elsewhere in thisdescription reference to directions is meant to be relative andexemplary; for example, horizontal and vertical are meant to indicateorthogonal relationship. Directions are exemplary and are used tofacilitate description and understanding of the invention.

[0147] The horizontally polarized light component 61 and the verticallypolarized light component 62, the directions of polarization beingrepresented by the dots 63 and the arrow 64, respectively, are incidenton the switch 11. Prom the switch 11 the light components 61, 62 areincident on the analyzer 12′. That light component which has apolarization direction that is parallel to the transmission axis of theanalyzer 12′ will be transmitted through the analyzer, and the otherlight component will be blocked. Depending on whether the switch 11 isin the operative state to transmit light without rotation of the planeof polarization or is in the operative mode to rotate the plane ofpolarization of the light transmitted therethrough, one or the other ofthe light components 61, 62 will be transmitted through the analyzer 12′at a respective location represented by one of the arrows 5 a, 5 b.

[0148] An exemplary use of the invention is illustrated in FIG. 7 forthe CRT display 2 or for a liquid crystal display 20, for example. Thedisplay 2, 20 has a resolution of some fixed number of raster lines orrows of pixels that are updated periodically, for example, 60 times persecond.

[0149] Assume that the speed of the display is increased, for example,is doubled to 120 times per second to re-scan the raster lines and/orthe rows of pixels. The switch 11 can be synchronized with the switchingof the display (CRT 2 or liquid crystal display 20) such that the rasterimages, for example, are alternately displaced and not displaced, e.g.,to locations 5 a and 5 b, respectively. Such synchronization may be withrespect to the blanking pulse or some other signal.

[0150] The amount of such shifting or displacement can be adjusted asaforesaid so that the displaced raster lines (or pixel rows)interdigitate the non-displaced raster lines (pixel rows). Theinformation on the displaced and non-displaced rasters (pixel rows) areselected to carry complementary information; and, therefore, theresolution of the entire image displayed by the optical display system 3or 13 is increased by a factor of 2. The same technique can be used toprovide image coverage over the dead space between adjacent pixels in aliquid crystal display (or in a CRT, e.g., where a shadow mask blockstransmission of electrons) or to cover areas where conductors or otherelectrical connections or components of a liquid crystal display, suchas parts of an active matrix array, are located, usually betweenadjacent pixels.

[0151] The display ordinarily would be refreshed or updated 60 times persecond to cover both the odd and even raster lines. However, byincreasing the refresh or update rate to 120 times per second and usingthe electro-optical dithering system to shift the location of the outputimage or optical signal for part of the time, essentially the odd andeven raster lines, while unshifted, can be refreshed or updated 60 timesper second and the odd and even raster lines, while shifted, can berefreshed or updated 60 times per second. The update or refresh times orrates presented here are exemplary; others may be used.

[0152] In FIG. 7, assuming the display 2 is a CRT, the front face 70 hasa plurality of odd raster lines and a plurality of even raster lines.During operation of the CRT display 2, initially the odd raster linesare scanned to produce a first subframe (field). Subsequently, the evenraster lines are scanned, and a second subframe (field) is produced. Theinformation produced during the respective first and second subframes isreferred to as complementary and together complete an image (sometimesreferred to as a frame or picture) that is viewed. The time betweenproducing one subframe and the next is sufficiently fast that the eye ofan observer (viewer) integrates the respective first and second subframeimages to see one complete (composite) image. Similarly, using theprinciples of the present invention, the space between adjacent rasterlines can in effect be scanned to produce additional complementary imageinformation. Thus, for example, the odd lines can be scanned during thefirst subframe; the even lines can be scanned during the secondsubframe; the odd lines can be scanned during a third subframe butduring which the switch 11 of the electro-optical dithering system 1 isoperative to cause shifting of the image to the space between respectiveadjacent pairs of odd and even raster lines; and finally during a fourthsubframe analogous to the third, the even raster lines can be scannedwhile the electro-optical dithering system provides a shift of opticaloutput, to produce the shifted image between respective pairs of odd andeven raster lines. In this way resolution of the output image producedby the optical display system 3 is increased without having to increasethe resolution or space between relatively adjacent raster lines (scanlines) of the CRT display 2 and a similar technique can be used toincrease the effective number of the pixels, pixel rows, etc. toincrease resolution of the liquid crystal display 20.

[0153] Turning to FIGS. 8 and 9, an auto-stereoscopic display system 80is shown using the electro-optical dithering system 1 of the invention.The principles of auto-stereoscopic display are well known and will notbe described in detail here. However, the technique of obtaining theauto-stereoscopic display effect will be described.

[0154] In the auto-stereoscopic display 80, there is a CRT display 2,which provides a light output 4, which is delivered to a linearpolarizer 12. The-plane polarized light from the linear polarizer 12 isprovided to the electro-optical dithering system 1, which includes asurface mode device (surface mode liquid crystal cell) switch 11 anddouble refracting material (birefringent material) 10. At the output ofthe electro-optical dithering system 11 is a cylindrical lens array 81.The cylindrical lens array includes a plurality of cylindrical lenseslocated in an appropriate arrangement or pattern, as is known, to directlight to or toward respective eyes 82, 83 of a person, or to some otherdevice able to detect or “see” the light received thereby. By providinga left eye image to the left eye 82 and a right eye image to the righteye 83, an individual viewing the auto-stereoscopic display system 80will discern a three dimensional or stereoscopic effect.

[0155] Using the electro-optical dithering system 1 of the invention incombination with a display source, such as a CRT display 2, a liquidcrystal display 20, or some other display, light beam steering can beaccomplished to obtain the left eye and right eye images. Therefore,auto-stereoscopic display systems can be provided easily and relativelyinexpensively.

[0156] In FIG. 9 the technique for obtaining beam steering forauto-stereoscopic effect is illustrated. Incident light 4, which isunpolarized, as is represented by the arrows and dots on the light isincident on the plane polarizer 12. Alternatively, plane polarized lightcan be provided from an image source or light source, such as a liquidcrystal display (and polarizer 12 may be eliminated). In any event, thelight which exits the polarizer 12 is plane polarized, for example, in ahorizontal plane, as is illustrated in FIG. 9. Such light then entersthe switch 11 and from there the light enters and transmits through thedouble refracting material 10. Depending on whether the switch 11rotates the plane of polarization or it does not rotate the plane ofpolarization of the light transmitted therethrough, the doublerefracting material 10 will deflect or will not deflect the lighttransmitted therethrough. In the case that the switch 11 does not rotatethe plane of polarization, and the above-described alignment of thedouble refracting material 10 is provided, the light will transmitdirectly through the material 10 without deflection as light ray 90.When light ray 90 is transmitted through the interface 91 between thecylindrical lens 92 of the cylindrical lens array 81 and the externalenvironment, such as air, represented at 93, the light 90 will refractin the direction of the arrow 94 toward the left eye 82 of the observer(viewer). The light 90 traveling in the direction of the arrow 94remains polarized in the so-called horizontal direction, i.e., into andout of the plane of the paper of the drawing.

[0157] However, when the switch 11 rotates the plane of polarization oflight transmitted therethrough, the double refracting material 10deflects the light, as was described above, resulting in the light 95,which travels to a different location of the interface 91 of the lens92. The light 95 refracts at the interface 91 and is bent or deflectedin the direction of the arrow 96 toward the right eye 83 of theobserver. The light 95 is vertically polarized, i.e., the plane ofpolarization is parallel with the plane of the paper of the drawing ofFIG. 9.

[0158] In operation of the auto-stereoscopic display 80, left eye andright eye images sequentially are produced by the display 2 (20) forexample. When the left eye image is displayed, the switch 11 does notrotate the plane of polarization, and the light 90 follows the directionof the arrow 94 to the left eye 82 of the observer. When the right eyeimage is produced by the display, the switch 11 does rotate the plane ofpolarization so that the material 10 deflects the light as light 95which is refracted to the direction of the arrow 96 to the right eye 83of the observer. For convenience of this description, it is understoodthat the indices of refraction of the material 10 and the material ofwhich the lens 92 is made would be the same or about the same to avoidfurther refraction at the interface therebetween; however, if there isrefraction there, such refraction can be taken into account, as will beappreciated by those having ordinary skill in the art.

[0159] Referring to FIGS. 10 and 11, a display system 99, which includesa liquid crystal display 100, is shown in top plan and top sectionviews. The display system 99 is similar to the several other displaysystems described herein, such as those designated 3, 13, etc. The LCD100 has a plurality of pixels 101 arranged in respective rows 102 withdead space 103 between respective rows and also at the edge 104 of thedisplay 100. As is seen in FIG. 11, the liquid crystal display 100includes a substrate 105 on which an active matrix array 106 is located.The liquid crystal display also includes a further substrate 107, aspace 108 between substrates where liquid crystal material 109 islocated, a seal 110 to close the space between the substrates, and (notshown) appropriate driving circuitry, as is well known. Light 120represented by respective arrows illustrated in FIG. 11 is provided by alight source 121 and is selectively transmitted or not through theliquid crystal display. The light 120 is plane polarized by a planepolarizer 122 located between the light source 121 and the liquidcrystal display 100, and the light 120 is transmitted or is nottransmitted as a function of the plane of polarization thereof relativeto an analyzer 123, as is well known. An electrode 124 on the substrate107 and respective transistors and electrodes of the active matrix array106 on the substrate 105 apply or do not apply electric field to liquidcrystal material 109 at respective pixels 101 to determine whether ornot the plane of polarization of light 120 is rotated and, thus, whethersuch light will be transmitted or will not be transmitted through theanalyzer 123.

[0160] The light 120 which is transmitted through the analyzer 123 isincident on the electro-optical dithering system (EDS) 1. Theelectro-optical dithering system may be operated to not shift or toshift the location of the light 120 to locations 5 a, 5 b in the mannerdescribed above. If the optical signal at locations 5 a, 5 b iscomplementary, as was described above, the resolution of the opticaldisplay system 99 shown in FIG. 11 can be increased. Moreover, as partof such increased resolution, the dead space 103 where transistors 131and/or other components that are not light transmissive in the activematrix array 106 effectively are covered over by the shifted light 5 b,for example. Therefore, using the electro-optical dithering system 1 ina display system 99 as described, the light blocking portions of theactive matrix array, of conductors, etc., can be in effect overcome ornegated while the overall resolution of the display is improved.

[0161] The parts shown in FIGS. 10 and 11 are in a relatively horizontalrelation showing dithering in a vertical direction. It will beappreciated that dithering can alternatively be in a horizontaldirection or, if desired, multiple electro-optical dithering systems 1can be used in optical series in order to obtain both vertical ditheringand horizontal dithering.

[0162] The LCD 100 preferably is relatively fast acting to turn on andoff. Therefore, using the combination of the fast acting LCD with theEDS 1 the respective lines of one subframe of information can bedisplayed by the respective rows of pixels of the LCD and subsequentlythe interlaced lines of the next subframe can be displayed by the samerespective rows of pixels of the LCD.

[0163] The light source for the LCD 100 may be a pulsed source, whichproduces light output in pulses or sequential bursts. In such case, itis desirable to synchronize the light pulses or bursts of the lightsource with the LCD and/or with the EDS 1. Therefore, the respectivepixels of the LCD would transmit or block light when the light source isproducing a desired light output. The amount of time that the lightsource is transitioning between a light transmitting or light blockingstate may be reduced and preferably is minimized. Also, the LCD would beoperative to transmit or to block light when the light source isproducing its intended light output rather than when the light source isnot producing a burst of light or a desired light output. This tends toincrease the contrast of the output image, since the shutter element(LCD 100) is not changing state when the light is pulsed, e.g. ischanging its state from light producing to not producing or vice versa.

[0164] The EDS I and the LCD 100 preferably are synchronized. Therefore,when the LCD is producing scan lines of information from one subframethe EDS is in one state, and when the LCD is producing scan lines ofinformation from the other subframe, the EDS is in its other statethereby causing the lines of one subframe to be interlaced with thelines of the other subframe. The EDS and a pulsating type light sourcealso may be synchronized so that the EDS switches states during the timethat no light output or non-optimal light output is produced by thelight source. This further enhances contrast of the display system 3,13, 99.

[0165] Various circuitry may be used to obtain the aforementionedsynchronization. Two examples are shown, respectively, in FIGS. 12 and13. In FIG. 12 an exemplary display system 140 is shown. In the displaysystem 140 a blanking pulse from a source 141 is supplied to respectiveLCD buffer and EDS buffer circuits 142, 143 to synchronize operation ofthem. The actual information signals from line 144 indicating the lighttransmitting or blocking state, for example, of the pixels of the LCD100, for example, as is shown in FIGS. 10 and 11, are provided the LCDbuffer 142. Those information signals are not delivered to the LCD 100,though, until appropriately coordinated or synchronized with theblanking pulses. The EDS 1 is connected to the EDS buffer 143 andreceives its drive signal from line 145 to dither or not the opticaloutput from the LCD 100. The EDS buffer also receives the blanking pulsefrom the source 141 to synchronize delivery of the signals to the EDSwith such blanking pulses and/or with the operation of the LCD bufferand information signals delivered to the LCD. The buffers 142, 143 canbe synchronized with respect to each other by appropriate timedoperation thereof with respect to the blanking pulse; or, alternatively,the buffers can be directly coupled to each other to synchronizeoperation thereof so that the dithering function is coordinated withswitching of pixels or writing of information to the LCD.

[0166] As another example of synchronization, FIG. 13 depicts a displaysystem 150 in which a pulsed light source 121, for example, receivespulsed power from a power supply 151. A signal representing thecharacteristics of the pulsed power from the powers supply 151 isprovided to the LCD buffer 142 and EDS buffer 143, which respectivelyreceive information and power signals on lines 144, 145 as describedabove. By synchronizing the LCD 100 and EDS 1 with respect to each otherand/or with respect to the pulsing light source, the LCD can switchstates as new information is written thereto when the light source isnot producing significant light output, and/or the EDS can switch fromdirect transmission to dithered transmission of light states when thelight source is not producing a bright output and/or the LCD is not inthe process of switching display states.

[0167] The foregoing are but two examples of synchronization useful inthe various display systems and embodiments of the invention. It will beappreciated by those having ordinary skill in the art that many othertypes of synchronizing techniques may be used to obtain the desiredsynchronization.

[0168] Although it may be desired to obtain full interlacing andseparation of respective lines as in a CRT display, for example, evenless than full interlacing, e.g., an amount of displacement that doesnot fully separate the lines but nevertheless reduces the amount ofoverlap thereof, will tend to reduce the above-mentioned jitter andimprove the optical output of the LCD.

[0169] Interlacing or dithering can be used to effect verticaldisplacement (changing of location of the optical output signal),horizontal (lateral) displacement, and/or diagonal displacement of theoptical signal, such as that produced as the output from a pixel of adisplay, e.g., a CRT, LCD, or any other type of display. The directionof displacement will depend on the orientation of the various componentsof the optical system. For example, in the EDS of FIG. 1 havingorientation of axes of components shown in FIGS. 4A, 4B and 4C, verticaldisplacement will occur. However, by changing the relative orientationof the axes by 45 degrees or 90 degrees, the displacement as a functionof the state of the switch 11, for example, can be changed to diagonalor horizontal.

[0170] Using the vertical displacement of optical signals by the EDS 1in combination with a display, such as an LCD, for example, it possiblein effect to double the resolution of the display in the mannerdescribed above. Thus, in a sense, the EDS becomes an optical linedoubler which doubles the number of horizontal lines of resolution ofthe display system. However, by using both vertical and horizontaldisplacement functions in a display system, it is possible to obtain ineffect up to quadruple the resolution of the display relative tooperation of the display absent the EDS.

[0171] Referring to FIGS. 14 and 15A-15E an EDS system 201 used with adisplay 202, in the illustrated embodiment an LCD (although other typesof displays can be used), is shown as a display system 203. In FIGS. 14and 15A-15E reference numerals which designate parts that are the sameor similar to those described above are the same as the referencenumerals that designate such above-described parts except beingincreased by the value 200. Thus, display system 203 is similar todisplay systems 3, 13, 99, etc. mentioned herein.

[0172] However, the EDS system 201 of display system 203 includes twoEDS portions 201 v and 201 h, which respectively can be operated toobtain vertical and horizontal displacement of the optical signaltransmitted therethrough. Each EDS 201 v, 201 h includes, respectively,a double refracting material 210 v, 210 h and a switch 211 v, 211 h. Forexample, each double refracting material may be a calcite crystal andeach switch may be a surface mode (birefringent) liquid crystal cell.The source of optical signals in display system 203 is a flat panelliquid crystal display 202, although other types of displays may beused. The LCD 202 provides light output that is plane polarized, and,therefore, a separate polarizer like the polarizer 12 of FIG. 1, forexample, may be unnecessary in the illustrated embodiment of displaysystem 203. It will be appreciated that although the display system 203uses two EDS devices or portions, the principles of the invention may beused with more than two EDS portions to obtain not only horizontal andvertical displacement but also displacement in even another direction.

[0173] The relative orientation of the axes of the respective componentsof the display system 203 is shown in FIGS. 15A-15E. Plane (linear)polarized light having a horizontal plane of polarization is provided bythe LCD 202, as is seen in FIG. 15A. In the vertical displacement EDS201 v, the axis of the birefringent liquid crystal switch 211 v shown inFIG. 15B is oriented at 45 degrees to the plane of polarization of lightfrom the source 203; in the illustrated embodiment, such orientation isactually −45 degrees relative to vertical, for example. The projectionof the axis of the double refracting material 210 v is vertical, as isseen in FIG. 15C. In the horizontal displacement EDS 201 h, the axis ofthe birefringent liquid crystal switch 211 v is oriented at +45 degreesto the vertical (FIG. 15D), and the projection of the axis of the doublerefracting material 210 h is horizontal (FIG. 15E). The actualalignments may be slightly different from those illustrated toaccommodate or to compensate for residual birefringence in the liquidcrystal switches and/or for other purposes. Also, if desired wave platesand/or other optical components may be included with one or more of theEDS devices 201 h, 201 v to compensate for such residual retardationand/or other factors.

[0174] The display system 203 can be operated in four different states.In one state shown in FIG. 16A with both EDS devices 201 v, 201 h ofFIG. 14 not displacing light, the light from the display source 202 istransmitted without being displaced; this may occur with birefringentswitches 211 v, 211 h being in high voltage, non-polarization rotatingstate and low, polarization rotating states, respectively. In a secondstate shown in FIG. 16B with EDS device 201 v, 201 h respectivelydisplacing and not displacing light, the light from the display source202 is transmitted while being horizontally, but not verticallydisplaced; this may occur with both birefringent switches 211 v, 211 hbeing in high voltage, non-polarization rotating state. In a third stateshown in FIG. 16C with both EDS devices 201 v, 201 h displacing light,the light from the display source 202 is transmitted while beingdisplaced both horizontally and vertically; this may occur with bothbirefringent switches 211 v, 211 h being in low voltage, polarizationrotating state. In a fourth state shown in FIG. 16D with EDS device 201v, 201 h respectively displacing and not displacing light, the lightfrom the display source 202 is transmitted while being vertically, butnot horizontally displaced; this may occur with EDS 211 v in the lowvoltage, polarization rotating state and birefringent switch 211 h beingin high voltage, non-polarization rotating state.

[0175] In FIG. 17 is illustrated a composite of the display conditionsdepicted in FIGS. 16A through 16D. By using relatively fast acting LCDas the display source 202 and two EDS devices 201 h, 201 v synchronizedand operated in the manner just described so that the pixels first areshown in the manner in FIG. 16A, then as in FIG. 16B, etc., sufficientlyquickly that the observer's eyes tend to integrate the respectiveimages, a high resolution image with a pixel density like that shown inFIG. 17 can be obtained. It will be appreciated that an exemplaryoptimum improvement in resolution using the display system 203 in thedescribed manner can increase resolution of the display 202 byapproximately a factor of 4.

[0176] Thus, it will be appreciated that the respective switches 211 v,211 h may be operated according to the following table to obtain theabove-described operation controllably to vertically shift or displaceand/or to horizontally shift or displace the optical signals from thedisplay 202. High means electrically operated so as to be notpolarization rotating and low means electrically operated so as to bepolarization rotating, although other conventions may be used. TABLE 1Switch 211v Switch 211h High Low High Low Low Low Low High

[0177] In the present invention the switches and double refractingmaterial may be substantially optically transparent. Therefore, thosecomponents do not tend to absorb light. The use of such components in adisplay system 203, for example, does not ordinarily significantlyreduce the brightness of the display output. Although two or more imagesare placed sequentially in the field of view provided by the displaysystem 3, 13, 99, 203, etc., brightness of the display output is notdiminished; rather, image resolution can be increased.

[0178] Other types of birefringent materials and/or devices may be usedin place of or in addition to the calcite material double refractingdevice 10 described above. For example, other types of crystal materialsand/or minerals may be used; the amount of displacement between anunrefracted optical signal and a refracted optical signal by such doublerefracting material would depend on index of refraction characteristicsof the double refracting material, the index of refraction of theenvironment external of the double refracting material, wavelength ofoptical signal, and distance the optical signal travels in the doublerefracting material.

[0179] Another double refracting material which may be used in theinvention as component 10, for example, is liquid crystal material.Liquid crystal material, such as nematic liquid crystal and smecticliquid crystal material may be birefringent and may be used. Other typesof birefringent liquid crystal materials also may be used. By organizingor orienting the liquid crystal material in a particular organization ororientation, the transmission of light therethrough with or withoutrefracting the light can be dependent on the direction of electricvector of the light, e.g., the plane of polarization of plane polarizedlight.

[0180] A polymer liquid crystal may be especially useful as such adouble refracting material, for such material both can have a relativelylarge birefringence and also can be formed into a solid material whichmaintains the orientation of the structure of the liquid crystalmaterial thereof. Polymer liquid crystal materials are known.

[0181] However, if the double refracting material were of a liquidcrystal material whose structural orientation or organization could beswitched, e.g., in response to application of a prescribed input such asan electric field (or removal of such field or changing voltage or someother characteristic of the field, etc.), then the function of the twocomponents of an EDS may be replaced by a single switchable liquidcrystal shutter type device. In this case the liquid crystal shuttercould provide one index of refraction or birefringence characteristic torefract light transmitted therethrough a given amount and a differentindex of refraction characteristic with no birefringence so as not torefract such light or with parameters to refract the light a differentamount.

[0182] An embodiment of display system 203′ which uses a pair ofswitchable liquid crystal cells 270, 271 associated with a liquidcrystal display 202′ is shown in FIGS. 18 and 19. Each of the liquidcrystal cells 270, 271 functions as a combination of birefringent ordouble refracting material 210 h, 210 v and as a switch 211 h, 211 v.The liquid crystal cells may be, for example, aligned like abirefringent liquid crystal cell using nematic or smectic liquid crystalmaterial between a pair of glass plates. The plates are treated so theliquid crystal is aligned generally in the same direction at both plateswithout twisting; and, therefore is so aligned throughout the cell. Theliquid crystal material preferably is tilted, e.g., at 45 degrees, toobtain a desired birefringence characteristic; but although tilted, theprojection of the axis of the liquid crystal structure would be in thesame plane as the plane of polarization of incident light thereon toobtain the desired birefringence characteristic. The exemplaryarrangement of axes of the display system 203′ is shown in FIG. 19.

[0183] By changing the electrical drive signal to the respective liquidcrystal cells 270, 271, the index of refraction characteristics thereofcan be changed, and, as a result, the location of the optical signaltransmitted therethrough can be changed, e.g., dithered as describedherein. For example, for plane polarized light incident on liquidcrystal cell 270 which has liquid crystal therein structurally alignedsuch that the light experiences the ordinary index of refraction of theliquid crystal and no birefringence, the light will transmit directlythrough the liquid crystal cell without refraction. However, if theliquid crystal is structurally aligned such that the light experiencesthe extraordinary index of refraction and, thus, birefringence, thelight will be refracted at the interface between the liquid crystalmaterial and the glass plate or the like forming or at one surface ofthe liquid crystal cell 270 at one side; and the light will be refractedagain at the interface between the liquid crystal and the glass plateetc. at the other surface of the liquid crystal cell so as to beparallel with the light incident on the liquid crystal cell 270 butdisplaced from the extension of the transmission axis of the incidentlight.

[0184] Thus, by selectively operating, e.g., energizing and deenergizingor changing energization level, the liquid crystal cells 270, 271, then,can change the location of the optical signal output by the displaysystem 203′. The liquid crystal should be aligned to present to thelight transmitted therethrough either the ordinary or extraordinary axisor index of refraction and appropriate birefringence characteristic asdescribed above. If only one liquid crystal cell 270 is used, theoptical signal can be changed back and forth in one plane or direction.If two liquid crystal cells 270, 271 (like the cell 270, for example)are used and are arranged such that the axes thereof are non parallel,then the optical signal can be changed back and forth in two planes ordirections. Such non-parallel alignment may be perpendicular alignmentto obtain up/down dithering and left/right dithering relationships.Since the plane of polarization of light incident on the liquid crystalcell 271 should be parallel to the axis of that cell, a half wave plate272 may be placed between the liquid crystal cells 270, 271 to rotatethe plane of polarization of the light exiting the liquid crystal cell270. For example, the axis of such half wave plate may be oriented at 45degrees relative to the plane of polarization, i.e., half way betweenthe 90 degrees desired rotation. It is noted that a polarizer 12 isshown in FIGS. 18 and 19; such polarizer helps assure the quality ofpolarization of the light from the display; but such polarizer can beeliminated if the output from the display is of sufficient quality ofpolarization, e.g., minimal amount of unpolarized light includedtherein.

[0185] The EDS 1, 201 may be used in a display system 3, 13, 99, 203,203′, etc. which is monochrome or multicolor. Operation for a monochromedisplay system would be, for example, as is described above. Oneembodiment exemplifying operation for a multicolor, such as a red, greenand blue (rgb), display system can employ the above-described type ofoperation for each color. Therefore, when one color or a group of colorsis being displayed by respective pixels of such a color display, theoptical signal output can be either transmitted without displacement orwith displacement in the manner described above. As is depictedschematically in FIG. 20, part of a display 202′, e.g., similar todisplay 202, is shown including three representative adjacent pixeltriads 281, 282, 283, each including a red, green and blue pixelportion. The display 202′ may be operated in a color frame sequentialmode in which respective red, green and blue frames or images areproduced in time sequence. In this case all red pixels of respectivepixel triads 281, 282, 283, etc. would be red where it is desired in thefinal image to have red light; subsequently green and then blue pixelsof the image would be created. Alternatively, the respective red, greenand blue pixels of respective triads can be displaying respective colorssimultaneously. In either case, the principles of the invention usingthe EDS 1, 101, etc. may be used to increase resolution of the outputimage in the above-described manner.

[0186] However, the EDS may be used for the purpose of selectivelydithering (displacing) less than all of the color frames of a multicolordisplay, especially if the display is operated in a color framesequential mode. For example, the dithering function can be usedselectively to displace or not the green optical signal (light producedduring the green frame) of the display 3, 13, 99, 203, 200′; however,the EDS may be used so it does not selectively to dither the opticalsignal during one or both of the other color frames. Since the human eyeis more sensitive to green light than to red or blue light, asignificant enhancement of the apparent resolution of the multicolordisplay can be achieved by only selectively dithering the green lightoptical signal. If desired, the green and red optical signals can beselectively dithered without selectively dithering the blue opticalsignal; and this will result in an even greater apparent resolution ofthe multicolor display than if only the green optical signal wereselectively dithered. Since the human eye is not as sensitive to bluelight as it is to red or green light, the fact that resolution of theblue light or blue frame component of the overall image is not enhancedby the dithering of the invention may not significantly reduce theresolution of the composite multicolor output image. By reducing theamount of dithering required, it is possible that the complexity and/orcost of the electronic drive and timing circuitry employed in theinvention can be reduced.

[0187] Referring to FIGS. 21, and 22A-22F, there is shown a schematicillustration depicting a time sequence of operation of the inventionusing a segmented display system 403. FIG. 22A represents the outputoperation of the display system 403 at one period of time; FIG. 22Brepresents operation at the next period of time; and so on. In FIGS. 21and 22A-22F the various parts which correspond to parts described aboveare identified by the same reference numerals but increased to a 400series. Thus, display system 3, 13, 99, 203, 203′, etc. in FIGS. 21 and22A-22F is designated 403, for example.

[0188] The face 470 of the display system 403 in FIGS. 21 and 22A-22F isdivided into three separate segments 470 a, 470 b, 470 c. Morespecifically, the display 402 may include a CRT or an LCD 2, 20, 102,etc., and between the display and the viewer, for example, is at leastone, and possibly several in series, electro-optical dithering system 1,11, 21, 101, as was described in the several embodiments above. Forsimplicity of description here the display system 403 is described withonly one EDS, though.

[0189] The EDS 401 includes, for example, a double refracting material410 and a switch 411 such as a surface mode liquid crystal cell.However, the switch 411 is segmented into several areas which can beseparately addressed to change the optical characteristics thereof. Theswitch 411 is shown in FIGS. 21 and 22A-22F as having three separatesegments 411 a, 411 b, 411 c; but it will be appreciated that the switchmay have fewer or more segments. Each segment 411 a, 411 b, 411 c can beseparately operated to change or not to change the direction of plane ofpolarization of light transmitted therethrough. Each segment can be aseparate liquid crystal cell or each can be part of the same liquidcrystal cell which has an electrode arrangement which permits operatingof the different parts separately.

[0190] In FIGS. 22A, 22B, 22C, respectively, (with reference also toFIG. 21) the first subframe (field) of information is writtensequentially to the upper, middle and lower thirds 402 a, 402 b, 402 cof the display 402 for direct transmission without being dithered orshifted in position. By the time the information is being written to themiddle third of the display 402, the information written to the topthird begins fading; and by the time the information is being written tothe bottom third, the information at the top third is substantiallyfully faded and that at the middle third is beginning to fade.

[0191] In FIG. 22D the start of information representing the secondsubframe (field) being written to the display 402, initially to the topthird 402 a of the display, is shown. The dithered information opticalsignal in the top third of FIG. 22D is represented by the illustrateddashed lines. Since such information is for the second subframe, theoptical signal output is intended to be dithered/changed; however, atthis time the image or optical output presented by the middle third 402b of the display 402 has not completely faded. Therefore, if the opticaloutput of the entire display 402 were dithered at this time, the opticalinformation or optical output signal still being displayed at the middlethird would be shifted to an incorrect location. To avoid this wrongfulshifting of the optical signal from the middle third at this time, onlythe top third 402 a of the display 402 is dithered. Preferably the topthird actually is dithered when the previous image there has faded; andthat actually can occur at the time period represented in FIG. 22C.

[0192] At the time period represented by FIG. 22D the middle third ofthe display 402 has faded, and is dithered; and at the time periodrepresented by FIG. 22E, information is written to that dithered middlethird of the display, and the bottom third which has faded is dithered.At the time period represented by FIG. 22F, the dithered imageinformation is written to the bottom third of the display 402 and thetop third is dithered since the information previously written there bynow has faded.

[0193] The above-described operation of the display system 403 cancontinue sequentially as the respective subframes are sequentiallydisplayed, e.g., the optical signals comprising such subframes arepresented as the output of the display system. In each subframe thedifferent respective parts or segments are sequentially dithered or notpreferably so that a segment is already undithered or dithered beforethe raster, line, row, etc. of information to form the optical signal iswritten to the respective pixels of that segment. The dithering orundithering switching action, e.g., operation of the respective switches411 a, 411 b, 411 c from one state to the other, also can be carried outas the action of writing information to a segment is carried out; butordinarily it would be better to effect the dithering or unditheringwhen the segment is relatively blank (e.g., information there has faded)to avoid undertaking a dithering or undithering action while an opticaloutput is being displayed.

[0194] It will be appreciated that the segmentation technique may beused with display system which uses a CRT display, a liquid crystaldisplay or some other type of display. The segmented switch 411 approachalso is useful to remove artifacts caused by a relatively slow actingLCD.

[0195] Further, it will be appreciated that the various EDS embodimentsof the present invention and display systems using such EDS embodimentsare operative to move, shift, translate, etc. an output optical signalfrom one location to another without substantially affecting brightnessof the display system or optical signal. The components of the EDSgenerally are optically transparent, and, therefore, other than arelatively minor amount of absorption of light transmitted therethrough,there may be otherwise relatively little reduction in light intensity.Therefore, the features of the invention may be used for the variouspurposes described herein, for example, to increase resolution, to coveror to reduce the effective optical dead space, etc., without reducingbrightness of the optical output.

[0196] A passive dithering system 500 in accordance with one aspect ofthe present invention is illustrated schematically in FIG. 23 in anoptical display system 501. The passive dithering system 500 as shown isused in connection with a display 502 which produces an output ofpolarized light, such as might be produced by a twisted nematic (TN)based flat panel liquid crystal display 504 incorporating a linearpolarizer 506 or by a CRT display with an added linear polarizerinterposed, as is the polarizer 506, between the CRT display and thedithering system 500. The dithering system 500 includes a pair of doublerefracting or birefringent material layers 508 h, 508 v, such as acalcite crystal material, separated by a half wave plate 510. A waveplate 512, such as a quarter wave plate, turns plane polarized lightinto circularly polarized light; circularly polarized light canmathematically be resolved into equal amplitudes of vertical andhorizontal plane polarization separated in phase by 90°. Thus, thequarter wave plate in a sense separates incident plane polarized lightinto relatively orthogonal plane polarized components for delivery tothe birefringent material 508 h as an input for the dithering system500. The effect of the passive dithering system 500 can be to enhancethe resolution of the display output by reducing fixed pattern noise inthe display. The passive dithering system 500 can increase the number ofoutput pixels provided simultaneously by an optical display system.

[0197] In FIG. 24a a very generalized example of the function of thepassive dithering system 500 is shown considering an image 520 a createdby a single pixel 520 of the flat panel liquid crystal display 504separated from adjacent pixels 522 in the display by optical dead space524. The birefringent material 508 h effectively creates a double image520 b of the image 520 a which is displaced or dithered in, for example,a horizontal direction, as is shown in FIG. 24b. The second birefringentmaterial 508 v, which receives both images 520 a and 520 b, creates asecond pair of images 520 c, 520 d displaced vertically from the firstpair of images as is shown in FIG. 24c. In this way, the image producedby a single pixel, such as exemplary pixel 520, can be made to fill orat least to increase the fill of the optical dead space 524 between thepixels 522 which is typically used to electrically isolate adjacentpixels and to accommodate circuitry and electrical components. In otherwords, the dithering system 500 increases the fill factor of the display502 as viewed. Therefore, the passive dithering system 500 expands orenlarges the respective pixels. In the example of FIGS. 24a, 24 b, 24 c,the pixel 520 a can be said to have been expanded or enlarged to coverthe area shown in FIG. 24c being occupied by images 520 a, b, c, d.

[0198] If desired, the locations at which the passively dithered orcreated images 520 b, c, d are placed may be other than or in additionto the optical dead space 524. For example, such image may be placed tooverlap another image or pixel, to overlap several images or pixels,image(s) and optical dead space, etc., for example, as is describedfurther below.

[0199] One possible manner of orienting the axes of the opticalcomponents of the passive dithering system 500 in the optical displaysystem 501 is shown in FIG. 25a. The linear polarizer 506 or polarizeddisplay output is oriented vertically so that an image of a pixelemerging from the polarizer or display will be linearly polarized in avertical direction, as is shown at pixel 520 a in FIG. 25b. In FIGS.25b-g the respective arrows represent direction or plane of polarizationof light. The quarter wave plate 512 is aligned with its axis 512′ at45° to the plane of polarization of the plane (linearly) polarized lightincident thereon, e.g., from the polarizer 506. With this arrangementthe quarter wave plate 512 converts the incident plane polarized lightto circularly polarized light. Circularly polarized light in effect canbe resolved into two orthogonal plane polarized components 520 a′, 520a″ which are out of phase by 90°, and such resolution is shown for pixel520 a in FIG. 25c. The birefringent material 508 h is arranged relativeto the linear polarizer 506 and quarter wave plate 512 with theprojection of its optic axis 508 h′ into the plane of the polarizer 506and quarter wave plate 512 being horizontal, e.g., parallel to thepolarized light component 520 a″ and perpendicular to the polarizedlight component 520 a′. The axis 510′ of the half wave plate 510 isoriented at +22.5 degrees to vertical, and the second birefringentmaterial 508 v is oriented with the projection of its optic axis 508 v′into the plane of the polarizer 506, etc. being vertical. It will beappreciated, however, that this arrangement is only one of many possiblearrangements of the axes of the components which would produce thedithering or pixel expanding or enlarging effect described herein and/orsimilar or equivalent effects.

[0200] With further reference to FIGS. 25a-g, which additionallyillustrates the path of an image through the passive dithering system500, the path of the exemplary pixel image 520 a through the system willbe described in greater detail. As oriented, the linear polarizer 506transmits optical information in the form of pixel images from pixels inthe display which have effected the light transmitted therethrough so asto be polarized in the direction of the transmissive axis 506′ of thelinear polarizer. For the exemplary image 520 a in FIG. 25b, the lightwould thus be polarized in a vertical direction represented by arrow 520a′.

[0201] Since the plane of polarization of the image 520 a is at a 45degree angle to the optic axis 512′ of the quarter wave plate 512, thequarter wave plate converts the plane polarized incident light tocircularly polarized light. The circularly polarized light can beresolved or considered as two plane polarized light components 520 a′,520 a″ (FIG. 25c) the planes of polarization of which are orthogonal andthe phases of which are 90° out of phase. It will be appreciated thatother means or techniques may be used to divide the plane polarizedlight, which is delivered to the birefringent material 508 h, intoplural components which are acted on differently by the birefringentmaterial, for example acted on in the manner illustrated in FIGS. 25a-gor in some other manner.

[0202] Since the plane of polarization 520 a″ of some of the lightrepresenting pixel 520 a in FIG. 25c, which is incident on thebirefringent material 508 h, is in the place of the optic axis 508 h′and encounters birefringence due to the tilting of the optic axis 508 h′as was described above, e.g., with respect to FIGS. 1-6, such light isrefracted by the birefringent material to form the pixel 520 b at alocation displaced, for example, to the right from pixel 520 a, as isseen in FIG. 25d. Also, since the plane of polarization 520 a′ of someof the light representing pixel 520 a in FIG. 25c, which is incident onthe birefringent material, 508 h, is perpendicular to the optic axis 508h′, the path of such light is not altered by the birefringent material,and pixel 520 a is located as is shown in FIG. 25d. Summarizing, as theorthogonally related polarized components pass through the birefringentmaterial 508 h, one of the polarized components will be refracted anddeflected horizontally while the other component will be unaffected. Asa result, the birefringent material 508 h will yield two images, animage 520 a in its original location and a horizontally displaced image520 b with the images being polarized orthogonally to one another.

[0203] The images 520 a and 520 b then pass through the next opticalcomponent in the passive dithering system 500, the half wave plate 510,where the plane of polarization of each of the images 520 a and 520 b iseffectively rotated +45 degrees so that the plane of polarization ofeach image is as shown in FIG. 25e. The polarizations represented byarrows 520 a″′ and 520 b″ for pixel images 520 a, 520 b in FIG. 25e arethe vector equivalents to the polarizations represented by therespective arrows 520 a′, 520 a″, 520 b′, 520 b″ for pixels 520 a, 520 bin FIG. 25f. Two of such vector equivalent polarizations of FIG. 25f areparallel to the optic axis 508 v′ of the second birefringent material508 v, and two are perpendicular to the optical axis 508 v′. Due to suchrelationships of the planes of polarization of each of the images 520 aand 520 b in FIG. 25f to the axis 508 v′ of the birefringent material508 v, the images 520 a and 520 b will be resolved into theirorthogonally polarized components 520 c, 520 d, respectively, as thesecomponents pass through the birefringent material 508 v. The polarizedcomponents of each image 520 a, 520 b which are parallel (520 a′, 520b″′) to the plane containing the axis 508 v′ will be refracted anddeflected vertically to result in images 520 c and 520 d while the otherpolarized components 520 a″, 520 b′, which are perpendicular to the axis508 v′ (or the plane containing that axis) will be unaffected. As aresult, the original image 520 a is dithered into four images 520 a, 520b, 520 c and 520 d. These images may be of substantially equalintensity.

[0204] While the passive dithering system 500 discussed above wasillustrated as doubling images in two directions, horizontal andvertical, a passive dithering system that doubles the image in only asingle direction only is also possible. Such a system may include asingle birefringent material used in conjunction with a displayproducing a polarized or non-polarized output to result in a doubledpixel image or to perform passive line doubling.

[0205] Also, it will be appreciated that the above description withrespect to FIGS. 23, 24a -c, and 25 a-g is exemplary, and otherarrangements of components to compose a passive dithering system toobtain a desired pixel enlarging, expanding, shifting, etc. may beemployed. For example, a birefringent liquid crystal cell may be used asa wave plate: a surface mode liquid crystal (e.g., U.S. Pat. No. Re.32,521) cell or a pi-cell liquid crystal cell (e.g., U.S. Pat. No.4,582,396) which is tuned to the desired retardation of quarter wave orhalf wave are examples. The birefringent material may be liquid crystalcells. Various crystals, prisms, or other devices may be used to providebirefringence and/or polarizing functions. By changing the amount ofbirefringence and optical path length through a birefringent materialthe amount of deflection of a pixel image can be determined. Changingrelative orientation of axis of one or more components can change thedirection a pixel is shifted. Of course, the illustrated alignment ofcomponents is relative and reference to vertical, horizontal, into orout of the plane of the paper or drawing only is for convenience ofdescription. All such equivalent and alternate or additional materialsand/or alignments of components and functional operation are consideredwithin the scope of the present invention.

[0206] As is evident from the description above with respect to FIGS.23-25 and the description below with respect to FIGS. 26-32, in anexemplary passive dithering system of the invention, birefringentmaterial may be used to change location of light representing a pixel,an image of a pixel, or another optical signal (for conveniencesometimes simply referred to as pixel). The passive dithering system,therefore, is able to change the apparent location of the pixel. Suchchange may result in an increase in or enlarging of the pixel size, in adoubling or duplicating of the pixel, etc.; such change in location maysimply be a change in the apparent location of the pixel without anydoubling, duplicating, changing of size, etc.

[0207] When the passive dithering system is used to dither a pixel tochange size, e.g., effectively to enlarge the pixel, the ditheringsystem may cause there to be multiple spaced apart pixels derived fromthe original pixel or pixels. Alternatively, one or more of the multiplepixels may overlap or be sufficiently adjacent to another pixel as to beconsidered touching or in any event not spaced apart. As an example, byenlarging a pixel to cover optical dead space of a display, the apparentresolution of the display usually is increased even without increasingthe actual number of pixels driven by the display.

[0208] In the case of a pixel being expanded using an exemplary passivedithering system according to the invention, light from the originalpixel is distributed over a viewed area that is larger than the area ofthe original pixel of the display. However, the total amount of lightreaching the eye of an observer, for example, remains substantially thesame as that provided by the original pixel before being expandedbecause the components of the passive dithering system are not the lightabsorbing or blocking type. Therefore, the apparent brightness of adisplay when used in combination with such a passive dithering systemwould tend not to be diminished.

[0209] The passive dithering system of the invention is described withrespect to several embodiments. These embodiments are examples ofcomponents and arrangements of components to obtain the passivedithering effect of the invention. Many other components andarrangements of components also may be used to obtain passive dithering,as will be appreciated by those who have ordinary skill in the art.

[0210] For example, in the embodiments of passive dithering systemsillustrated in FIGS. 23-27 a half wave plate is used to set upparticular plane polarization conditions, such as direction of plane ofpolarization; and in the embodiments illustrated in FIGS. 28-32 aquarter wave plate is used to set up particular plane polarizationconditions. In the embodiments of passive dithering systems illustratedin FIGS. 23-25 and 28-30 the passive dithering systems receive planepolarized light input from a liquid crystal display that provides planepolarized light output or from another display which may not provide aplane polarized light output but which is used in combination with aplane polarizer to obtain the desired polarized light input to thedithering system. However, in the embodiments illustrated in FIGS. 26,27, 31 and 32 the passive dithering systems receive and operate onunpolarized light.

[0211] The components of the respective passive dithering systemsdescribed with respect to FIGS. 23-32 are arranged to expand a singlepixel or light forming that pixel to four pixels which are arranged in atwo by two rectilinear array, such as that depicted by pixels 524 a-d inFIG. 24c. However, it will be appreciated by those who have ordinaryskill in the art that the passive dithering systems of the invention maybe adjusted, including changing of optical axes orientations, changingof birefringence value, adding or deleting components, etc., to expandthe single pixel to fewer or to more than four pixels and to arrangethose pixels in a rectilinear array or in another pattern orarrangement. Also, although quarter wave plates and half wave plates aredisclosed useful in passive dithering systems, it will be appreciatedthat other types of wave plates or appropriate means may be used, too.Preferably the wave plates and/or other appropriate means provide thesame or substantially the same wave plate function, such as opticalretardation, for all, for a relatively wide range of wavelengths oflight or at least for the wavelength range intended to be used.

[0212] Using the principles of the invention to expand a pixel formed ofplane polarized light, the incident plane polarized light is dividedinto two orthogonally related plane polarized components. A quarter waveplate may be used for this function. A quarter wave plate having itsoptic axis aligned at 45° to the plane of polarization of incident planepolarized light converts the plane polarized light to circular polarizedlight, which can be resolved to orthogonally related plane polarizedcomponents which are of equal amplitude but are out of phase by 90°. Ifthe quarter wave plate is oriented at other than 45° to the plane of theincident plane polarized light, the output therefrom will beelliptically polarized, which also may be resolved to respective planepolarized components possibly with phases that differ by other than 90°and/or amplitudes which are not equivalent. Means other than a quarterwave plate also may be used to effect such separating of the incidentplane polarized light into respective distinguishable components. Theincident plane polarized light, which is resolved to respectivedistinguishable components, is directed to the birefringent material,which separates the components in effect by directing them to differentlocations and thereby expands the apparent area of the pixel.

[0213] For unpolarized light input to a passive dithering system of theinvention used, for example, to expand a pixel, the incident light isdirected to birefringent material usually without the need to planepolarize the incident light. Since the incident light already includesor can be considered as being resolved to two orthogonally related planepolarized components, the birefringent material separates the respectiveorthogonally plane polarized components in effect by directing them todifferent locations and thereby expands the apparent area of the pixel.

[0214] Referring to FIG. 26, there is shown a passive dithering system500′ of an optical display system 501′ used in connection with a display532 which produces non-polarized (unpolarized) light, such as a nematiccurvilinear aligned phase liquid crystal (NCAP), polymer dispersedliquid crystal (PDLC) or liquid crystal polymer composite (LCPC) basedflat panel liquid crystal display. The passive dithering system 500′ ofFIG. 26 includes the same optical components as the dithering system 500described above relative to FIGS. 23-25, such as a birefringent material508 h, a wave plate 510 and a second birefringent material 508 v. Inthis instance, neither the passive dithering system 500′ nor the display532 is provided with a linear polarizer to polarize the output lightfrom the display.

[0215] In operation, the passive dithering system 500′ when used inconnection with a display producing non-polarized light will result inhorizontal and vertical pixel image doubling similar to that produced bythe passive dithering system 500 and shown in FIGS. 23-25. In fact, theorientations of the optic axes 508 h′, 510′ and 508 v′ of the components508 h, 510, 508 v, shown in FIGS. 26 and 27 may be the same as whenthose components are used in connection with a display producing apolarized output. (If it were desired to use the dithering system 500with an unpolarized light producing display 532, the polarizer 506 couldbe placed optically between the display 532 and the dithering system 500in the manner shown in FIGS. 23-25, for example).

[0216] One possible set of orientations for the optic axes of thesecomponents is shown in FIG. 27. The optic axis 508 v′ of the firstbirefringent material 508 v is vertical and is tipped as was describedabove, the axis 510′ of the half wave plate 510 is at +22.5° to verticaland the projection of the optic axis 508 h′ of the second birefringentmaterial 508 h into the plane of the page is horizontal and is tipped aswas described above. Although the light which enters the firstbirefringent material 508 v is non-polarized, it can be visualized aspolarized light resolved into two orthogonal components such as avertical and horizontal polarized component as shown by arrows in theexemplary pixel image 534 a created by a corresponding pixel 534 in thedisplay 532.

[0217] The components 508 v, 510 and 508 h then function basically asdescribed above in FIG. 25. The first birefringent material 508 v willresolve the individual components of the pixel image 534 a into theirorthogonal components and will dither (shift location of) one polarizedcomponent relative to the other polarized component to produce avertically displaced double image of the pixel image 534 a. The halfwave plate 510 will then rotate the polarization components of thoseimages as in FIG. 25e so they are at 45° angles to the optic axis 508 h′of the second birefringent material 508 h where the images will bedoubled and displaced in a horizontal direction as in FIG. 25g. As aresult, the initial image 534 a is doubled in the vertical direction andthen the initial image and the doubled image are doubled in thehorizontal direction to produce four adjacent images which maysubstantially cover the portion of the original pixel 534 a in thedisplay and dead space surrounding the pixel in one vertical andhorizontal direction.

[0218]FIG. 28 illustrates an alternate embodiment of a passive ditheringsystem 540 of an optical display system 541 shown with an opticaldisplay which produces linearly polarized output light, such as by atwisted nematic based flat panel liquid crystal display 542incorporating a linear polarizer 544. The passive dithering system 540includes a first birefringent material 546 v, a second birefringentmaterial 546 h and quarter wave plates 548, 549, respectively,interposed between the source of polarized light (display 542 and, ifused, polarizer 544) and the first birefringent material 546 v andbetween the birefringent materials 546 h and 546 v. One possible set oforientations for the axes of the linear polarizer 544 of the display,the birefringent materials 546 v and 546 h and the quarter wave plates548, 549 is shown in FIG. 29. The linear polarizer 544 has atransmissive axis in the vertical direction. The projection of the opticaxis of the first birefringent material 546 h into the plane of thetransmission axis of the linear polarizer also is vertical, i.e.,parallel to the axis of the polarizer. The axes of the quarter waveplates 548, 549 are oriented +45° to vertical and the projection of theoptic axis of the second birefringent material 546 h into the plane ofthe linear polarizer is at +90° to vertical, i.e., horizontal.

[0219] The passive dithering system 540 functions basically the same wayas the passive dithering system 500 is described above relative to FIG.25. The function of the half wave plate 510 in the passive ditheringsystem 500 has been replaced in the system 540 by a quarter wave plate549. The quarter wave plate 548 and birefringent material 546 v functionas the quarter wave plate 512 and birefringent material 508 h of FIGS.23-25. The quarter wave plate 549 effectively divides the polarizedlight components of light passing through the wave plate 549 byconverting the light to circularly polarized light and its respectiveequivalent orthogonal plane polarized components like the quarter waveplates 512, 548 do. The components of the circularly polarized light arethen dithered by the second birefringent material 546 h in a horizontaldirection as explained above for the passive dithering system 500. Oneadvantage of using the quarter wave plate 549 as opposed to the halfwave plate 510 or 510′ is that the quarter wave plate 549 will tend tointroduce less chromatic aberration on the light passing therethroughsince a quarter wave plate usually is thinner material than a half waveplate and, therefore, usually is less dispersive, e.g., exhibits lessoptical dispersion.

[0220] In FIGS. 30a-30 e are shown the operation of the passivedithering system 540 of FIGS. 28 and 29. In FIG. 30a a pixel 542 a ofdisplay 542 is shown. Light from pixel 542 a is vertically polarized andis represented by the vertical arrow therein. The linear polarization isproduced by the display 542 and/or is due to the polarizer 544. Aseparate polarizer 544 ordinarily is unnecessary if the display 542produces polarized light output. Optical dead space 550 surrounds thepixel 542 a.

[0221] The quarter wave plate 548 divides the vertically polarized lightfrom the polarizer 544 to obtain two orthogonal plane polarizedcomponents, as is seen in FIG. 30b. In FIG. 30c it can be seen that thebirefringent material 546 v changes the location of the verticallypolarized light component portion of light incident thereon moving thatlight vertically relative to the location of the vertically polarizedlight component portion. Therefore, pixel 542 a is expanded, e.g., isdoubled, in that pixel area 542 b now has been created. The quarter waveplate 549 divides (resolves) the plane polarized light from thebirefringent material 546 v so that each pixel 542 a, 542 b has bothorthogonal plane polarized light components, e.g., horizontal andvertical, as is shown in FIG. 30d. In the manner described above, thedouble refracting material 546 h expands, e.g., doubles, the pixels 542a, 542 b to create pixel areas 542 a, 542 b, 542 c, 542 d shown in FIG.30e.

[0222]FIGS. 31 and 32 illustrate a passive dithering system 540′ whichis identical to the passive dithering system 540 shown in FIGS. 28-30but it is used in an optical display system 541′ with a displayproducing non-polarized (unpolarized) output light, such as an NCAP,PDLC or LCPC based flat panel liquid crystal display 560 e.g., like thedisplay 532 and pixels 534 of FIGS. 26 and 27. The orientation of thebirefringent materials 546 v and 546 h and the quarter wave plate 549,which are represented in FIG. 32, may be the same as those described forthe like components for the passive dithering system 540 although itwould be appreciated that this is only one possible set of orientationsfor the axes of the components which would dither an image in the mannerdescribed above. The passive dithering system 540′ functions inbasically the same way described above for the system 540 but onunpolarized input light, which is resolved as orthogonally related planepolarized light components (see the description above concerning FIGS.26 and 27), as opposed to the linearly polarized light which the system540 receives from the display 542.

[0223] It also will be appreciated that the several features andembodiments of the invention illustrated and/or described herein may beused with other features and embodiments that are illustrated and/ordescribed herein as well as equivalents thereof. For example, in thesegmented display system described the EDS may be formed by a calcitecrystal and a surface mode liquid crystal cell, by a calcite crystal anda twisted nematic liquid crystal cell or by some other type of switchand/or some other type of double refracting material. Also, the EDS maybe a liquid crystal EDS in which both the switch function and the doublerefracting function can be carried out by the same device, e.g., as inthe embodiment of FIGS. 18 and 19. Moreover, in many instances passivedithering systems may be used in conjunction with or as a substitute forsome of all of the components described for the EDS. These are simplyexamples of combining features and it will be appreciated that othercombinations also may be made consistent with the spirit and scope ofthe invention.

[0224] From the foregoing it will be appreciated that variousembodiments of the invention using principles described herein may beemployed with polarized light or unpolarized light. If it possible tooperate based on an unpolarized light as an input to the ditheringsystem, e.g., using an NCAP display, there is no need for a polarizerand the undesirable effect that a polarizer has in blockingapproximately 50% of the transmitted light. It also will be appreciatedthat in various embodiments described herein a quarter wave plate may beused, a half wave plate may be used, and/or. a combination thereof maybe used. In various embodiments a half wave plate may be substituted forone or more quarter wave plates and vice versa. A quarter wave plate maybe used to convert plane polarized light to circular polarized light orto orthogonal components of plane polarized light. A quarter wave platealso may be used to convert plane polarized light to ellipticallypolarized light. A half wave plate is used to rotate the plane ofpolarization of plane polarized light. Usually the half wave plate willrotate the plane of polarization by twice the angle between the plane ofincident plane polarized light and the axis of the half wave plate.

[0225] Turning to FIG. 33 an active dithering system 601 is used with adisplay 602 in an optical display system 603. The dithering systemincludes a birefringent material 610, such as a calcite crystal, havingan axis 610′ that is oriented at an angle theta relative to horizontal,as is depicted in FIG. 33. The dithering system 601 also includes aswitch 611, such as a birefringent liquid crystal cell of the typedescribed above. The display 602 may be a liquid crystal display thatprovides plane polarized light output that has a vertical plane ofpolarization represented by the arrow 602′. Alternatively, the display602 may provide other than plane polarized light output, and in thatcase a plane polarizer 612 may be used to provide such verticalpolarization of the light delivered from the display and polarizer tothe switch 611. The orientation of the axis of the birefringent liquidcrystal switch 611 is at 45° to the vertical plane of polarization 602′,as is represented by the arrow 611′. As was described, as the switch 611is energized or not, the plane of polarization of the light outputtherefrom will be the same as the direction of the arrow 602′ or not,i.e., vertical, or horizontal. A half wave plate 615 between the switch611 and the birefringent material 610 has its axis 615′ oriented at anangle relative to horizontal that is ½ theta.

[0226] With reference to FIGS. 33 and 34, which presents representativeoperation of the dithering system 601, when the light transmittedthrough the switch 611 has a given plane of polarization, such lightwill be transmitted through the half wave plate 615 and birefringentplate (calcite) 610 to appear at the same relative positions as theyoriginally appear in the display 602. If such pixels are, respectively,red, green and blue pixels of a triad, such pixels may be at thelocations of the pixel images 620 r, 620 g, 620 b shown in FIG. 34.However, when the plane of polarization of the light exiting the switch611 is such that it is appropriately rotated by the half wave plate 615so as to impinge on the calcite 610 in a direction relative to the axis610′ to cause shifting of the light output, such pixels will appear asimages 620 r′, 620 g′, 620 b′. Thus, it will be seen that the offset orshifting is in a sense diagonal rather than horizontal or vertical. Theangle at which such diagonal occurs relative to horizontal, for example,depends on the magnitude of the angle theta. Thus, it will beappreciated by appropriately selecting the angles of the respective axisof the components and their relationship to each other, whereas desireddirections of shifting can be obtained. Also, the extent or distance ofsuch shifting can be determined, for example, by the thickness of thebirefringent device 610, i.e., the effect of optical thickness thereofhaving an affect on the light transmitted therethrough.

[0227] Referring to FIGS. 35 and 36 and the Chart I below, an opticaldisplay system 640, which includes two active dithering systems 641, 642and one passive dithering system 643 is illustrated. The optical system640 receives plane polarized light input 644 from a display 645. If thedisplay 645 is not the type that provides a plane polarized lightoutput, than an additional polarizer 646 may be used to provide suchplane polarization. The orientation of respective components of thedisplay system 640 is depicted by respective double-headed arrows abovethe various components.

[0228] The display system 640 may be used to provide a video outputdisplay operation. In an exemplary video display system, such as an NTSCor PAL system, it is conventional to compose a picture or a frame fromtwo interlaced and sequentially presented fields (sometimes referred toas sub-frames). The optical display is able to produce four outputconditions and signals in the manner described below. Such four outputconditions may correlate to two respective frames and the two respectivefields in each frame in a video display system, such as a televisionsystem using a liquid crystal display or some other display as the imagesource. However, it will be appreciated that the four output conditionsdescribed below may be correlated with the operation of other types ofdisplay systems or with a video display system in a way different fromthe exemplary operation described below.

[0229] In the optical system 640 the active dithering system 641includes a switch 650 and a birefringent device 651. The activedithering system 642 includes a switch 652 and a birefringent device653. The passive dithering system 643 includes a quarter wave plate 654and a third birefringent device or material 655. The first and secondswitches 650, 652 may be respective surface mode birefringent liquidcrystal cells or some other switch as is described elsewhere herein. Thefirst, second and third birefringent devices 651, 653, 655 may becalcite material or some other birefringent material having axisoriented generally in the manner illustrated and tipped in the mannerdescribed above.

[0230] In describing operation of the optical display system 640,reference is made to a pixel of the display and light representing thatpixel. The passive dithering system 643 effectively doubles the size ofthe pixel received by it from the display 645 and via the respectiveactive dithering systems 641, 642. Therefore, as is seen in FIG. 36,each pixel input to the passive dithering system 643 is shown in solidlines and the doubled image thereof is shown in dotted lines adjacentthereto. For example, the pixel provided the passive dithering system643 for the first field of the first frame is represented at 660, andthe dithered image 660′ is shown adjacent thereto in dotted lines. Thepassive dithering system operates in the manner of the passive ditheringsystems described above, for example.

[0231] Referring to the Chart I below, at frame 1, field 1, the voltageor energization of the first switch 650 is low so that the switchrotates the plane of polarization of the input vertically polarizedlight to horizontally polarized light as the output therefrom; see thecolumn labeled “polarization direction output 1” having the letter “H”representing such horizontal polarization. Delivery of that horizontallypolarized light to the first calcite 651 results in no shift oflocation. Continuing in the first line for frame 1, field 1 in the ChartI below, the voltage of the second switch 652 is low, whereby thatswitch rotates the plane of polarization back to vertical, as isrepresented by the letter “V” in the column labeled polarizationdirection output 2; and, therefore, the second calcite member 653 doesnot shift the location of the pixel. When the vertically polarized lightoutput from the second calcite 653 enters the quarter wave plate 654,such light is divided into horizontal and vertical polarized components;the vertically polarized component transmits through the third calcitematerial 655, and the horizontally polarized component is shiftedhorizontally thereby effectively doubling the size of the pixel andproducing the image 660′, as is represented in the last column of thetable designated calcite 3 shifting and doubling in the horizontaldirection the particular pixel.

[0232] The second field of the first frame, for example, each pixel ofthe second frame, is displaced vertically relative to the correspondingpixel of the first field of the first frame. The pixel 661 representsthe location of such downwardly vertically displaced pixel for thesecond field of the first frame when the display system is a video typeusing interlaced fields to produce a frame. The second line of the ChartI below shows the conditions of the surface mode switches 650, 652, bothbeing at high voltage so as not to rotate the plane of polarization oflight transmitted therethrough, the resulting vertical downwarddisplacement caused by the first calcite 651, and the doubling of thepixel by the passive dithering system 643 to produce not only pixel 661but also the dithered pixel 661′. In pixels 660, 660′, the two digitsone in each represent, respectively, first frame, first field; and inthe pixels 661, 661′, the digits one and two represent first frame,second field, respectively.

[0233] Lines three and four of the Chart I below represent conditionsand shifting resulting from those conditions of the switches 650, 652,direction of plane of polarization, etc. as was described above withrespect to the first two lines of the Chart I below in order to achievepixels 662, 662′ and 663, 663′, the primed pixels representing thedithered images that doubles the effective size of the overall pixel,such as the doubled size 663 plus 663′. As was mentioned above, theamount of shifting or translating of a particular pixel may be afunction of the birefringence and/or optical thickness of the respectivebirefringent device, such as the respective calcite plates 651, 653,655. Also, in a conventional video system there usually is no horizontalinterlacing. The two field of the second frame represented by pixels662, 662′, 663, 663′ may represent images moved to fill optical deadspace, images to effect super imposing respective colors, as isdescribed further below, or some other purpose. The increasinglyeffective size of each pixel, such as by doubling it to increase pixel660 to the effective size of the sum of pixels 660, 660′, can be used toimprove resolution by effectively covering optical dead space in thedisplay. The vertical displacing of pixels can be used to cause a liquidcrystal display to provide a true or more nearly true interlacedoperation whereby a pixel presented in one field of a frame is presentedat a different location when the second field of that same frame isproduced.

[0234] An advantage to the use of a dithering system with a display,such as a liquid crystal display, wherein the location of a pixel in theoutput can be shifted even though the actual location of the pixel inthe display itself, such as an LCD, remains fixed is that correct datacan be used to drive the pixel to provide the desired image output withrelatively accurate following of the video signal. In a conventional LCDused to provide a video output a particular pixel may average the twofields of a frame; the average is not an accurate representation of thedata received from the video signal. However, using a dithering systemin accordance with the present invention, a pixel of the LCD may bedriven based on information from the video signal intended to drive thatpixel for a particular field of a frame to provide a visual output fromthe display system, such as display system 640. Subsequently when theimage output of the respective pixel is shifted so that it is in thelocation desired for the second field of the particular frame, theactual information from the video signal that ordinarily would be used,say in a CRT, for example, could be the information that is used tooperate or to drive the pixel which then provides a relatively accurateoutput representative of the appropriate input signal.

[0235] Using the two active and one passive dithering systems of theoptical display system 640 is it possible to obtain eight copies of theoriginal image, if desired, namely that provided at pixel 660, forexample. Such eight copies may be obtained for every field for everyframe, if desired and, thus, provide a macro pixel effectively abouteight times the size of the pixel 660. In another embodiment, the datapicked off the incoming analog signal or other video signal thatoperates the pixel 660, e.g., to turn it on or off, may be selected atthe appropriate time to drive the pixel 660; and subsequently the pixel661 may be operated as a function of information picked off the incomingvideo or analog signal representing the desired operation of the pixel661 for interlaced fields operation of a conventional NTS or PAL system.However, additionally, if desired, the information from the incomingsignal also could be picked off to represent the on/off or intensityeffect of a pixel presented at location of pixel 662 accurately torepresent that pixel even though that pixel physically may not be in thedisplay 645 but rather is represented by the pixel of the display 645that produces pixel image 660 shifted to the location of pixel 662. Inother words, in an exemplary LCD there may be two relatively adjacentpixels, and the information from the incoming video signal would bepicked off from that video signal to drive the respective pixels at theappropriate times. However, there also may be information contained inthe video signal that would represent a desired optical output from theoptical display system 640 from a pixel located between the twomentioned pixels. The present invention allows the information from thevideo signal that would be used to drive such intermediate pixel to bedelivered to the pixel of the display 645 that would produce pixel image660 while the dithering systems in the optical display system 640 effecthorizontal or lateral displacement of the optical output to a locationwhere such intermediate pixel might otherwise appear in the output imagefrom the optical display system 640. This operation can enhance theresolution provided by the optical display system 640 and the accuracyof representation of the information carried by the input video signal,etc.

Superimposed Color Operation

[0236] Referring to FIG. 37 there is a shown a layout of an exemplarygroup of red, green and blue pixels of an exemplary liquid crystaldisplay. The pixels are arranged in respective parallel rows andcolumns. Capital letters represent the color of the pixel, e.g., whetherthe pixel will deliver output like that is red, green or blue. Portionsof two rows are shown.

[0237] In the viewing of a color liquid crystal display the eye of theviewer, i.e., a human eye, may receive light input from many differentpixels, and the eye effectively integrates the light inputs. One way ofconsidering such viewing is to analogize the adjacent pixels, which areextremely small, effectively being superimposed so that the lighttherefrom is superimposed. Therefore, the combination of red, green andblue light that is superimposed would provide a white light as seen bythe viewer.

[0238] The various embodiments of dithering systems in accordance withthe present invention, including those disclosed and equivalentsthereof, may be used to effect real superimposing of respective pixels,thereby enhancing the color output or color response of a color liquidcrystal display. Such superimposition is depicted in FIG. 37 and now isdescribed. The two rows of pixels shown in FIG. 37 are portions ofrespective rows of pixels in a color liquid crystal display. In thefirst row shown there are five pixels of the indicated colors; and inthe second row there also are five pixels of the indicated colors. Thesequence of colors is red, green and blue in both rows, but the sequenceis offset by one pixel one row to the other. Therefore, in the first(top) row the first pixel row, and in the second row the first pixel isgreen. The arrangement of pixels in FIG. 37 is exemplary. Many othertypes of arrangements of pixels may be used whether in parallel rows andcolumns in the manner shown, in a so called delta configuration orpattern wherein there is an offset of rows, such as in FIG. 40, etc.

[0239] Using the optical display system 640, for example, the red pixelRa at the top left of FIG. 37 is duplicated by the passive ditheringsystem 643 to produce a red pixel or ra, which is represented in dashlines. Operation of the first dithering system 641 produces a secondcopy of both those red pixels displaced downward to locations of dashred pixels designated ra′. Such operation of the first dithering system641 is coordinated with the second dithering system 642 to effect suchdownward shift. Similarly, horizontal shifting of all four red pixelsjust mentioned, namely Ra, ra, and the two designated ra′ to ahorizontally shifted or laterally shifted place results in the redpixels represented by dash lines and designated ra″, one of which issuperimposed over the green pixel Ga and one of which is superimposed onthe blue pixel Ba. Such shifting may occur in a time sequence that issufficiently fast that the human eye does not perceive the variousshifts. Additionally, such shifting occurs in a time sequencecoordinated with the desired color output from the display asrepresented by the input video signals to the display so that thesuperimposed colors provide a good quality and accurate representationof the color output from the display intended as a result of the inputvideo signal. Similarly to the just described shifting of the red pixelRa, shifting of the green pixel Ga also occurs, and such shifted pixelsare represented by dotted outline at pixel locations represented by Gadue to the passive dithering system 643, and the other shifted pixelsrepresented by dotted lines labeled ga′ and ga″ resulting fromcoordinated operation of the active dithering systems 641, 642.Furthermore, similar operation occurs for the blue pixel Ba, which isrepresented by phantom lines at pixels or pixel locations designed ba,ba′, and ba″. The four blue pixels represented by respectivedesignations ba′ and ba″ near the bottom of FIG. 37 would overly or besuperimposed on other pixels which are not shown in order to simplifythe drawing and description.

[0240] Briefly referring to FIG. 38, shifting of the red pixel R intorespective gaps and also superimposed on other pixels is shownschematically and simply. Specifically, pixel R is doubled by thepassive dithering system 643 of the optical display system 640 in FIG.35, for example to provide pixel r. Both pixels R and r are duplicatedalso at pixel image locations r′ shown in FIG. 38 in the gap betweenrespective parallel rows of actual pixels. Pixels R, r and r′ also areduplicated to the right relative to the illustration of FIG. 38 as pixelimages r″, some of which are in the same gap as pixel images r′ and oneof which overlies or is superimposed on the green pixel G. Thus, it willbe seen that the pixels can be shifted to various locations in thedisplay to achieve the desired optical output.

[0241] As the display of FIG. 38 is operated as part of the opticaldisplay system 640 to duplicate pixel images and/or to translate pixelimages, so, too, the display shown in FIG. 39 represents similarmodified operation of the optical display system 640. In particular, inFIG. 39 lateral shifting occurs like that in FIG. 38; but in FIG. 39 thevertical shifting of images results in the shifted image overlying thegap between adjacent rows of pixels of the display 645 and alsooverlying at least a portion of the pixel of the display 645 which isvertically displaced beyond such gap between pixel rows. Placing thepixel image in a gap increases the fill factor of the display. As wasmentioned above, the shifting may result in superimposing pixel imagesto achieve the superimposed color response described above. Also, ifdesired, the vertical shifting may result in a portion of the shiftedpixel image still overlapping a portion of the image in the originalrow, such as the illustrated pixel R and shifted pixel image r′therebelow. Such superimposing of pixels may provide a desired type ofvisual output for the optical display system 340.

[0242] Briefly referring to FIGS. 40 and 41, there is shown a deltadesign of pixel layout for a display in FIG. 40, such as an LCD 645 andthe output images therefrom after transmitting through an opticaldisplay system 680, which includes one active dithering system 681 andtwo passive dithering systems 682, 683. The active dithering system 681includes a switch, 684, such as a birefringent liquid crystal cell, anda calcite crystal 685 able to transmit an image or to shift the imagevertically ½ pixel, depending on the direction of plane of polarizationof light incident thereon. The passive dithering system 682 includes ahalf wave plate 686, which rotates the plane of polarization of incidentlight 45 degrees, and a second calcite crystal 687, which can transmitthe incident pixel image and has a thickness, birefringence, axialorientation and tipped to displace the image ½ triad pitch horizontally.The passive dithering system 683 includes a half wave plate 688, whichrotates the plane of polarization of incident light 45 degrees, and asecond calcite crystal 689, which can transmit the incident pixel imageand has a thickness, birefringence and axial orientation and tip to beable to displace the image 1 pixel pitch horizontally.

[0243] The optical display system 680 and dithering systems 681, 682,683 thereof are set up to effect shifting ½ triad pitch to the right; 1pixel pitch left and ½ pixel vertical pitch down. This arrangement isrepresented by only the blue pixel Ba. In shifting that pixel ½ triadpitch to the right, pixel ba results. In shifting both pixel Ba and ba 1pixel pitch to the left, two respective pixel images ba′ areproduced—one is superimposed over the green pixel G, and one is in thegap between the blue pixel Ba and the red pixel R horizontally adjacentto the blue pixel Ba. Such shifting provides both for filling theoptically dead space and effecting a superimposing of respective colorpixel images as was described above. The shifting of pixel imagesvertically to form the four pixel images ba″ places some of those in thegaps between rows of pixels and some in superimposed relation to thesame and/or other pixels or shifted pixel images.

[0244] Referring to FIG. 42, a person 704 is shown wearing a headmounted viewing system 705 in accordance with the present invention. Theviewing system may be part of a virtual reality viewing system havingone or more displays which are viewed by the person. The viewing systemmay be part of a telecommunications system, entertainment system, orsome other device in which light, optical, etc. information can bepresented for viewing, projecting, photographing, or other use.Exemplary systems in which the invention may be used are disclosed inthe above-mentioned patent applications; of course there may be otheruses, too.

[0245] The head mounted viewing system 705 includes a housing 705 h inwhich the various components of the viewing system 705 are included, anda mounting device 705 m, such as a strap, eyeglass or goggles type framesupport structure, etc. The mounting device 705 m mounts the housing 705h for support from the head of the individual 704 placing the viewingsystem 705 in position in front of one of the eyes for viewing of animage presented by the viewing system 705. Whether the viewing system705 is hand held, head mounted, or otherwise supported, for example,from a pedestal, tripod, frame, etc., from a table, from the floor, froma console 9, etc., preferably the viewing system 705 and housing 705 hthereof is relatively small and sufficiently lightweight to facilitatemoving, transporting, mounting, and/or holding. If the viewing system705 is to be hand held or head mounted, it especially should berelatively lightweight to avoid being a weight burden on the hand orhead of the individual using the viewing system 705. Also, to facilitateholding the viewing system 705 manually or head mounting the viewingsystem, the viewing system 705 should be relatively small. An exemplaryviewing system may be, for example, approximately 4 to 5 inches inheight, approximately 2 to 3 inches wide, and approximately 1½ to 2inches deep. These are exemplary only, and it will be appreciated thatother dimensions may be used.

[0246] In using the viewing system 705 it may be head mounted, handheld, coupled to a control box, console or the like, for example,similar to the main body of the conventional telephone when used in atelecommunication system.

[0247] Turning to FIG. 43, the viewing system 705 is shown in detail asa monocular viewing system. The housing 705 h includes a viewing portion711 and a support portion 712. The viewing portion 711 is intended to beviewed by an eye 713 of a person 704 (FIG. 42), and the support portion712 is intended to be held in the hand of that individual. As wasmentioned above, a head mount 705 m may be provided to support theviewing system 705 from the head of a person. Thus, the housing 705 hmay be hand held, supported by a strap, cap, temple piece as ineyeglasses, or otherwise mounted for viewing by a person.

[0248] The viewing system 705 includes an optical system 714 in thehousing 705 h. The optical system 714 includes an image source 715, suchas an LCD, that provides images for viewing by the eye 713 through aviewing port 716. A viewing lens 717 (or group of lens) presents to theeye 713 an image which appears at a comfortable viewing distance, suchas about 20 inches or more away. An image resolution enhancing device 18(sometimes referred to as an optical line doubler or OLD, ditheringdevice or system, EDS, etc.) optionally included in the optical system714 may be used to enhance the resolution or other qualities of theimage produced by the image source 715.

[0249] A number of optical components 720 are included in the opticalsystem 714. The optical components include focusing optics 721(sometimes referred to simply as “lens” or as projection optics or as aprojector), a beam splitter 722, and one or more retroreflectors 23,23′.

[0250] The image source 715 includes a display 724 d and a source ofincident light 724 i. The light source illuminates the display 724 d,and the display in turn presents images which can be projected forviewing by the eye 713, as will be described in greater detail below. Itwill be appreciated that other types of image sources may be used,examples being cathode ray tube displays, other liquid crystal displays,plasma displays, etc. Examples of several displays and light sources arepresented in the above-referenced co-pending patent applications. Aconnection cable 28 provides electrical and/or optical signals and/orpower to the optical system 714, and is particular to the image source715 and OLD 18 to develop the above-mentioned images for viewing by theeye 713. A control system 729 is coupled to the cable to provide suchelectrical signals for controlling operation of the display system 705,as is described in further detail below.

[0251] Summarizing such controlled operation, though, the display 724 dmay be a twisted nematic liquid crystal display, and the OLD 18 includesan optical switch, such as a surface mode liquid crystal cell, thatswitches polarization characteristics of light to cause the light outputto viewed by the eye 713 to be, for example, of enhanced resolution, asis described further below. Therefore, the control system 729 providessignals to generate the image by the display 724 d; and the controlsystem 729 also controls the optical switch to effect a synchronizationsuch that there is a phase or time delay between the signals to thetwisted nematic LCD and the signals to the optical switch. Accordingly,the optical switch which operates at a different speed, e.g., faster orin shorter time than the twisted nematic LCD will be coordinated withthe operation of the twisted nematic LCD to improve operation andoptical output of the display system 705. Detailed operation of thecontrol system is described further below, for example, with respect toFIGS. 44-46 and 48.

[0252] Dithering may refer to the physical displacement of an image. Thedithering system 718 may be an electro-optical dithering system (EDS),which refers to an electro-optical means to physically shift or tochange the location of an optical signal, such as an image. The shiftingmay result in doubling of the number of pixels or scan lines of adisplay—thus, reference to OLD (optical line doubler). The shifting alsomay result in quadrupling (or more or less increase) pixels or scanlines; and in such case OLD also may be used as a generic label. Theshifting may be active in response to an electrical, magnetic or otherinput. The dithering system 718 may be passive, e.g., in which shiftingoccurs constantly or substantially constantly (or continuously); inother words such shifting may occur all the time without the need for aseparate input to cause shifting. Various embodiments of ditheringsystems useful in the invention are described above.

[0253] The image may be shifted along an axis from one location toanother and then back to the first, e.g. up and then down, left and thenright, or both, etc. The optical signal may be moved in anotherdirection. The dithering may be repetitive or periodic or it may beasynchronous in moving an image from one location to another and thenholding it there, at least for a set or non-predetermined time. Also, aswas mentioned, the dithering may be passive, and, thus, constant, e.g.,without changing. When the dithering is passive there usually areprovided simultaneously the original image at the undithered locationand a second or dithered image at another location, e.g., locatedadjacent or spaced apart from the undithered image.

[0254] Referring to FIG. 44, the top line A in the graph represents anelectrical signal, namely the voltage applied to a given display pixel(sometimes referred to as picture element or component) as a function oftime. The pixel may be a part of a twisted nematic type LCD, such aspart of the display 724 d, especially an active matrix LCD, although thepixel may be a part of some other type of display, optical device, etc.When the voltage is applied to an active matrix display, it results inan electric field being applied across the liquid crystal materialcausing a particular type of operation, e.g., alignment with respect tothe field or when no field is applied relaxing to an alignment which maybe influenced, for example, by the surfaces, surface coatings, etc., ofthe liquid crystal cell or device forming LCD. The voltage A illustratedin FIG. 44 is applied at a frequency of 60 Hz.

[0255] The second line B in FIG. 44 represents the desired lighttransmission characteristic of an ideal pixel as a function of time. Inthe illustrated example, the pixel is switched between clear (sometimesreferred to as the white state) and dark (sometimes referred to as theblack state). As illustrated, the clear state would occur when thevoltage A is high, and the dark state would occur when the voltage A ishigh.

[0256] In the illustrated case of an ideal pixel in FIG. 44, the pixelswitches transmission B from dark to clear at the same time the voltageswitches from high to low. That is, the ideal pixel switches in phasewith the applied voltage A. Furthermore, in the OLD or EDS 1, etc.(FIGS. 1, 2-6, 11-12, etc.) hereof (hereinafter referred to as EDS 1 forbrevity although such reference includes the various embodiments ofactive and passive dithering systems disclosed herein), the position ofthe pixel changes by switching the voltage applied to the surface modebirefringent liquid crystal cell, optical switch or polarization rotator11 (FIGS. 1, 5 and 6, for example). Therefore, it follows that in theideal case, i.e., for use with the ideal pixel, the voltage applied tothe optical switch 11 also would be switched synchronously with thevoltage A applied to the ideal pixel and in phase.

[0257] However, a real liquid crystal display 20, 724 d utilizing thetwisted nematic effect cannot switch between transmission states asrapidly as indicated in the second line B of FIG. 44. For example, theactive matrix liquid crystal display used in the Sony XC-M07 monitor canswitch from dark to clear in about 20 milliseconds and from clear todark in about 11 milliseconds. Switching time is defined conventionallyas the time required for the transmission to change between 10% and 90%of the final values. This real switching behavior is illustrated in thethird line C of FIG. 44. In this third line C depicting lighttransmission, the transmission of the clear state has been normalized to100% and the transmission of the dark state has been normalized to 0%.It will be appreciated that the graph line C is schematic only, and theprecise times mentioned above are not necessarily accurate.

[0258] In FIG. 45 the graphs present information similar to thatpresented in the graphs of FIG. 44 except that in the graphs of FIG. 45the frequency of the applied voltage A′ to the pixel, e.g., of thedisplay 724 d, is doubled to 120 Hz. The transmission B′ of the idealpixel in FIG. 45 is shown synchronized and in phase with the appliedvoltage A′. However, the actual transmission C′ of a real pixel isillustrated in the third line of FIG. 45. As is shown, within theavailable time of respective half cycles of the applied voltage A′, thereal pixel is able to switch transmission between about 25% and 75%.This means that the contrast ratio would be reduced by a factor of aboutone half (½) compared to the 60 Hz case of FIG. 44. This behavior ischaracteristic of many twisted nematic effect LCDs; starting at amodulation of about 60 Hz. every increase in the frequency of theapplied voltage by a factor of two (2) usually results in a reduction inthe contrast ratio by a factor of about one half (½).

[0259] Referring to FIG. 46, line A″ represents the applied voltage tothe pixel at 120 Hz. The second line C″ represents the transmissionresponse of a real pixel of an active matrix twisted nematic LCD. Notethat line C″ is similar to line C′ in FIG. 45. A guide line D has beendrawn in the graph of line C″ in FIG. 46 at 50% transmission. Thatportion of a particular frame, in which the real pixel is presenting animage of clear or dark, having a transmission greater than 50% isdefined here as the clear state. That portion of the frame having atransmission less than 50% is defined here as the dark state. As seen,the real pixel does shutter light at 120 Hz but the transmissionmodulates between 25% and 75% rather than the 0% to 100% experiencedwhen the frequency of the applied voltage signal A was 60 Hz. in FIG.44.

[0260] Another feature of the 120 Hz response of the real pixel is shownin FIG. 46. Consider the point marked along the time scale by the doubleheaded arrow E. The bottom part of the arrow E indicates the point intime that the transmission of the real pixel switches from dark toclear; the top of the arrow E indicates the corresponding appliedvoltage. It can be seen that the applied voltage A′ is out of phase withthe transmission characteristics of the pixel, i.e., when the real pixelswitches between what is considered the clear state and the black state,by 90°.

[0261] In the present invention the EDS 1 may be adjusted to introduce asimilar phase shift in the voltage F (FIG. 46) applied to the opticalswitch 11. An exemplary optical switch 11 is a surface mode birefringentliquid crystal cell. Such device usually can switch between states inresponse to a change in input signal much faster than does a twistednematic liquid crystal cell or LCD. Therefore, by introducing theindicated phase shift in the driving of the surface mode liquid crystalcell and the twisted nematic LCD, the optical switch can be coordinatedto switch optically at the same time that the LCD 724 d, for example,switches optically from what is considered its clear state to what isconsidered its dark state or vice versa. As a result, as the EDS 1operates in coordination with the LCD 724 d, for example, to crispnessor sharpness of the output image can be improved and there is lesslikelihood of a bleeding effect between images produced by pixels whichare periodically optically shifted using the dithering principles of anOLD or the like.

[0262] After the phase of the surface mode liquid crystal cell opticalswitch 11 has been adjusted as described, the contrast of the display724 d would be reduced by a factor of about one half (½) when thedisplay is optically doubled and one fourth (¼) when the display isoptically quadrupled. The decrease in contrast is due to the increasedfrequency at which the display liquid crystal cell (LCD) is driven, notdue to the EDS or how it is driven. It has been found that the contrastreduction is nearly undetectable by the human eye and, therefore, hasbeen found acceptable for many applications.

[0263] It will be appreciated that although the above descriptionregarding FIGS. 44-46 presents phase shift of 90° for the indicatedpurpose, the principles of the invention may be used to introduce otherphase shifts to achieve a similar coordination between two opticaldevices which have different response characteristics, such as, forexample, change in light transmission or polarization as a function ofchange in electrical input, or other input, e.g., magnetic input.

[0264] In FIG. 47 details of optical components of the optical system714 of the display system 705 are shown. The optical components shown inFIG. 47 are similar to those included in the housing 705 h of FIG. 43;however, in FIG. 47 the housing 705 h and support 705 m are not shown tofacilitate illustrating the invention and to simplify the drawing.

[0265] The optical components 720 of the optical system 714 includefocusing optics 721 (sometimes referred to simply as “lens” or asprojection optics or as a projector), a beamsplitter 722 andretro-reflector 723. The display system 705 also may include an imagesource 715 (FIG. 43) which provides images or light havingcharacteristics of an image and, if desired, may be part of thementioned projector. An exemplary image source is a liquid crystaldisplay, such as a small liquid crystal television having across-sectional display area on the order of about one square inch orless. As shown, the image source 715 includes a liquid crystal display724 d which modulates light from the light source 724 i to form imagesfor viewing by the eye 713. Alternatively, the image source may beseparate and simply used to provide one or more images or light havingimage characteristics that can be provided by the viewing system 705,such as that shown in FIG. 1, or a head mounted display, sometimesreferred to as HMD to the eye 713. Additional optical components of theoptical system 714 may include linear polarizers, circular polarizers,wave plates, focusing elements, such as lenses or mirrors, prisms,filters, shutters, apertures, diaphragms, and/or other components thatmay be used to provide a particular type of output image for viewing bythe eye 713. Examples of several embodiments using such additionaloptical components are described below with respect to other drawingfigures.

[0266] The invention is useful with virtually any type of image sourceor display source. An example of such a display source is a compact flatpanel display, and especially one utilizing a reflective liquid crystaldisplay made from a single crystal silicon active matrix array.

[0267] In FIG. 47 the image source 715 displays an image 825, which isshown in the drawing as an arrow 826. The light 827 leaving the imagesource 724 represents an image or has characteristics of an image, andthat light is collected by the focusing optics 721 of the optical system714 of the display system 705 and travels to the beamsplitter 722. InFIG. 47 and in a number of the other drawing figures hereof the focusingoptics 721 is represented as a single lens. However, it will beappreciated that the focusing optics 721 may include one or more othercomponents, such as lenses, reflectors, filters, polarizers, waveplates, etc.

[0268] Although the image source(s) 715 is shown in FIG. 47 locatedrelatively above the beamsplitter 722, the image source mayalternatively be located below the beamsplitter as is shown in FIG. 2.

[0269] At least some of the light 827 a incident on the beamsplitter 722is reflected by the beamsplitter as light 827 b toward theretro-reflector 723. The retro-reflector may be, for example, a screenmade of retro-reflecting material. Exemplary retro-reflectors are wellknown. One example is that known as a corner reflector or a sheet havinga plurality of corner reflectors. Another example is a material havingplural glass beads or other refracting and/or reflecting devices on orin a support. An example of a retro-reflector is a film or sheetmaterial having a plurality of corner cubes which material is sold byReflexite Corporation of New Britain, Connecticut. Such material isavailable having about forty-seven thousand corner reflectors per squareinch.

[0270] The light (light rays) 827 c, which are shown as broken lines,are reflected by the retro-reflector 723 such that their path is exactlyback along their direction of incidence on the retro-reflector. In thisway some of the light rays 827 c pass through the beamsplitter 722 andare directed toward a location in space designated 828 in theillustration of FIG. 47. The eye 713 of a viewer (person) can be placedapproximately at location 828 to see the image, and the pupil and lens,individually and collectively designated 713 a, of the eye, accordingly,are shown at that point. The lens 713 a focuses the light incidentthereon as an image on the retina of the eye 713.

[0271] The projection lens 720 projects light toward the retro-reflector723 to cause a real image to be formed at the retro-reflector or infront or behind the retro-reflector. As is defined in Jenkins & White,Fundamentals Of Optics, McGraw-Hill, 1976, for example, using anexemplary projection lens, an image is real if it can be visible on ascreen. The rays of light are actually brought to a focus in the planeof the image. A real image is formed when an object is placed beyond thefocal plane of a lens; the real image is formed at the opposite side ofthe lens. If the object is moved closer to the focal plane of the lens,the image moves farther and is enlarged. In contrast, a virtual imageoccurs if an object is between the focal point of a lens and the lensitself.

[0272] In FIG. 47 the broken lines represent light rays which travelafter reflection by the retro-reflector along the same or substantiallythe same path, but in the opposite direction to, respective incidentlight rays impinging on the retro-reflector. Thus, the retro-reflector723 is part of a conjugate optics path 823 a in which light incidentthereon is reflected in the same path and opposite direction asreflected light. The beamsplitter 722 directs light from the focusingoptics 721 into that conjugate optics path and toward theretro-reflector; and the beamsplitter also passes light in the conjugateoptics path from the retro-reflector to the output port 16 (FIG. 2) forviewing by the eye 713. The beamsplitter 722 and retro-reflector 723cooperate as a conjugate optics system to provide that conjugate opticspath.

[0273] Using the described conjugate optics path and system, relativelyminimal amount of the light from the image source 724 and focusingoptics 721 is lost and, conversely, relatively maximum amount of lightis directed to the eye 713. Also, there is substantial accuracy of imageand image resolution conveyed to the eye. Furthermore, especially if arelatively good quality retro-reflector is used so that the preciselocation at which the image 830 is in focus will not be critical, e.g.,it can be behind or in front of the retro-reflector, the tolerancerequired for the relative positioning of the components of the opticalsystem 714 is less severe. This makes the HMD display system 705relatively robust and reliable.

[0274] In FIG. 47 the viewed image 830 is represented by an enlargedarrow 831. Such arrow 831 is shown in FIG. 47 as a magnified focusedimage of the image 825 from the image source 724. The image 830 may bein focus at or approximately at the retro-reflector 723, and this isespecially desirable for good quality images to be provided the eye 713when a relatively low quality retro-reflector is used. A low qualityretro-reflector is one which has relatively low resolution or accuracyof reflecting light in a conjugate manner in the same path but oppositedirection relative to the incident light. With a low or poor qualityretro-reflector and the image not being focused at the retro-reflector,it is possible that too much light may be lost from the desiredconjugate optics path back to the eye 713, and this can reduce thequality of the image seen. However, the image 830 may be in focus atanother location or plane either behind the retro-reflector (relative tothe eye) or in front of the retro-reflector, and this is easier to dowhile maintaining a good quality image for viewing when theretro-reflector is a good quality one. The better the retro-reflector,the more self-conjugating is the optical system 714 and the less theneed to focus with precision at the retro-reflector.

[0275] Retro-reflector quality may be indicated by the radians of beamspread of light reflected. For example, a relatively good qualityretro-reflector may have from zero or about zero radians of beam spreadto a few milliradians of beam spread. The quality usually is consideredas decreasing in proportion to increasing beam spread of reflectedlight.

[0276] In considering the brightness of the image seen by the viewer,the nature of the beamsplitter 722 plays a role. The light produced bythe image source 724 may be polarized or unpolarized. If thebeamsplitter 722 is of a non-polarizing type, then a balanced situationis to have 50% of the light incident on the beamsplitter 722 bereflected and 50% transmitted. Thus, of the light 827 a incident on thebeamsplitter 722, 50% is reflected and sent toward the retro-reflectorscreen 723 as light 827 b. Of the reflected light 827 c from theretro-reflector 723, 50% of the light will be transmitted through thebeamsplitter 722 and will travel to the viewer's eye 713. Thisconfiguration of the optical components 720 of the display system 705can transfer to the viewer's eye a maximum of 25% of the light producedby the image source 724. If desired, the beamsplitter 722 can bemodified in ways that are well known to change the ratio of thereflected light to transmitted light thereby. Also, the beamsplitter 722may include an anti-reflection coating so that all or an increasedamount of the image comes from one side of the beamsplitter and thus toreduce the likelihood of a double image.

[0277] Since the optical system 714 of the display system 705 providesgood resolution of the image and maintains the characteristics thereof,the image source can be a relatively inexpensive one that does not haveto compensate for substantial loss of image quality that may occur inprior display systems. Furthermore, since a relatively large amount ofthe light provided by the image source 724 is provided to the eye 713for viewing, e.g., since the retro-reflector can virtually focus thelight for viewing at the eye, additional brightness compensation forloss of light, as may be needed in prior display systems, especiallyportable, e.g., hand held or head mounted, ordinarily would not berequired.

[0278] For exemplary purposes, in FIG. 47 three light rays 840 a, 840 b,840 c (collectively 840) originating at the tip of the arrow 826constitute a portion of the light 827. Three light rays schematicallyshown at 841 a, 841 b, 841 c (collectively 841) also are examples oflight emanating at the tail of the arrow 826. The light 827 hascharacteristics of the image 825 from or provided by or at the imagesource 715, and represented by the exemplary light rays 840 and 841, isfocused by the focusing optics 721 onto the retro-reflector 723. Thesize of the image 830 seen as the arrow 831 on the retro-reflector 723depends on the focal length of the focusing optics 721 and the distancesbetween the image source 724 and the retro-reflector 723 from the focalpoints 843, 844 of the focusing optics 721. Thus, magnification candepend on such focal length. The image source 715 should be locatedrelative to the focusing optics 721 such that an image can be focused,e.g., in focus as is shown in FIG. 47, at or approximately at theretro-reflector. For example, the image source 715 may be beyond thefocal point 843 of the focusing optics 721, and the retro-reflectorlikewise preferably is beyond the focal point 844 of the focusing opticsso that the image can be focused at the retro-reflector.

[0279] In the illustration of FIG. 47 the image 830 on theretro-reflector 723 is magnified relative to the size of the image atthe image source display 724 d; it does not have to be magnified. Theimage 830 may be the same size as the image 825 or it may be smaller.Thus, although the image source display 724 d may be relatively smalland/or may provide a relatively small size image 825 at its output, thesize of the image 830 viewed by the eye 713 may be different.

[0280] The optical system 714 is operable to place the image planeeffectively at the retina of the viewer's eye 713. This is accomplishedby effectively putting the plane of the eye lens (or pupil) 713 aeffectively at the position occupied by the focusing optics 721 relativeto the source of the image provided to the focusing optics. In a sensethe lens 721 is optically superimposed on the lens 713 a of the eye 713.

[0281] The invention provides an optical system in which there areconjugate paths from a lens, such as focusing optics 714, whichcorresponds to the “lens means” of an optical sensor, e.g., the eye 713.Stated in another way, the invention presents visual information oroptical data with a wide field of view by taking the output from a lens(focusing optics 721) and reflecting the light back along a conjugatepath toward a location corresponding to that of the same lens which wasin the original path, but actually direct that reflected light onto theeye placed at such corresponding location. This is obtained by using theconjugate optics arrangement disclosed herein.

[0282] The human eye is most comfortable when viewing an image at adistance of about twenty inches, approximately at the distance at whichone would place a book, document, etc. to be read. It is desirable thatthe final image as seen by the viewer be located at such distance, e.g.,approximately twenty inches from the pupil 713 a of the eye. This can beaccomplished in the manner, if desired, by adding an additional lens 717(FIG. 43) or other optical system (not shown) between the beamsplitter722 and the eye 713. Such lens may cause the person to see a virtualimage behind the retro-reflector, as is described in several of theabove patent applications. Although in many viewing devices furtherspacing between the eye and the optical component of the optical systemnearest the eye may be desired to obtain desired eye relief, the use ofthe lens 717 at the indicated distance of about ½ to 1 inch from the eyeusually is acceptable and reasonably comfortable because that is theapproximate spacing of ordinary eye glasses to which people ordinarilyrelatively easily become accustomed.

[0283] The function of the lens 717 may be obtained by using a negativelens at the focusing optics 721.

[0284] Referring to FIG. 14 an EDS 201 in the form of an electro-opticaldithering system which includes two line doublers in optical series isshown used with a display 202, in the illustrated embodiment an LCD(although other types of displays can be used), as a display system 203.The display 202 and the EDS 201 may be substituted for the display 724 dand EDS 1 in the display system 705 of FIGS. 42 and 43. The display 202may include a light source or a separate light source 724 i may be usedto illuminate the display 202.

[0285]FIG. 48 presents a number of graphs representing signals in thecontrol system 729 for the display system 705 or display system 203 topresent an image that is enhanced by optical dithering (optical linedoubling, in fact quadrupling) and that is enhanced by the phaseshifting of the invention as described herein. The respective signalsare shown on a time scale presented on the “x” axis. Vertical syncpulses G from a conventional video signal used for driving a television,CRT, LCD, etc., are presented at periodic intervals, e.g., at afrequency of 60 Hz. (one pulse each about 16.67 milliseconds (ms)). Anodd/even frame signal H also is presented; this signal is approximatelya square wave having high and low half cycle portions, each half cycleoccurring over a period of about 16.67 ms. The high portion of the framesignal represents an odd or even frame, and low represents the otherframe. A video data delay signal I controls delivery of video data; highis on and low is off.

[0286] In the display system 203 there are two surface mode liquidcrystal cells 211 v, 211 h, hereinafter sometimes abbreviated SMD (forsurface mode device), which serve as respective polarization rotators oroptical switches. It will be evident that other types of switches may beused. As is known, one type of operation of an SMD results in the SMDhaving two states, one in which it provides substantially no opticalphase retardation of light, for example, zero or near zero, and one inwhich it provides a relative maximum amount of optical phaseretardation, for example, 90 degrees, 45 degrees, etc., depending on theoptical thickness of the SMD and/or on other properties of theparticular SMD. Usually the minimum and maximum optical phaseretardations are produced, respectively, when a respective relativemaximum and minimum voltage is applied across the liquid crystal cellforming the SMD. Usually, the minimum voltage is a non-zero rms voltagewhich preconditions the liquid SMD crystal cell, sometimes referred toas biasing the SMD, to help maintain the alignment of the liquid crystalmaterial in the maximum optical retardation condition. In one example,the preconditioning is provided by a constantly applied voltage in the“low voltage” or maximum optical retardation state. In another example,the precondition is provided by the effect of an rms voltage occurringas a result of periodically driving the liquid crystal cell with avoltage that varies between an instantaneous value of a maximum leveland zero. In this case, the voltage is reapplied before the liquidcrystal cell can relax fully. Other techniques for driving an SMD alsomay be possible.

[0287] As is seen in curve J, the voltage waveform applied to the SMD211 v (FIG. 14) varies at the extremes J′ between −15 volts and +15volts which provides minimal optical phase retardation (rotation of theplane of polarization). Portions J″ of the voltage J also are at plusand minus a small voltage that is slightly above and below,respectively, the zero voltage level; these portions J″ are the voltageof the SMD when it is in the maximum optical phase retardation condition(providing maximum rotation of plane of polarization). Each portion J′and J″ of the voltage J is the same duration as the respective halfcycle of the odd/even signal H and the same duration as the time periodbetween vertical sync pulses G. However, the phase of the voltagewaveform J is shifted from the phase of the vertical sync G and odd/evenframe signal H by an amount which is determined in the manner describedabove with respect to FIGS. 44-46, for example. That phase shift in theillustrated example is 13.2 milliseconds, as is evident from the scaleat the bottom of FIG. 48. Waveform signal or voltage K in FIG. 48 isapplied to the SMD 211 h (FIG. 14). It varies only at one half (½) thefrequency of the waveform J.

[0288] As an example of operation of the display system 203, which isnot necessarily coordinated with the sequence of FIGS. 16A-16D, althoughproducing the result of FIG. 17, incident plane polarized -light isprovided to and transmitted through the SMD's 211 h and 211 v, which areoperated generally according to the waveforms J and K. Therefore, thepolarization of light respectively entering the birefringent crystals,e.g., calcite or other birefringent material, 210 h, 210 v will varygenerally in the manner depicted by curves L and M, which issynchronized and in phase or approximately in phase with the operationof the SMD's 211 h, 211 v. As light transmits through the respectivebirefringent crystals 210 h, 210 v, the location of the image fromrespective pixels of the display 202 will vary generally along the linesof the curves N and O. The description herein refers to direction, e.g.,horizontal and vertical; it will be appreciated that such reference onlyis exemplary, and where vertical shifting or orientation is referred to,horizontal could be substituted, and vice versa.

[0289] The phase shifting for coordination of optical switching with anoptical display, for example, as described above, also may be used in adisplay system that provides multicolor output with good contrast eventhough brightness or intensity of the output light is varied, forexample, of the type disclosed in above-referenced patent applicationSer. No. 08/187,163. Using such phase shifting in coordination with theliquid crystal display system of such patent application and/or with thedithering of others of the patent applications referenced above toprovide a multicolor output can increase the resolution, sharpness andcrispness of the viewed image, for example.

[0290] Referring to FIG. 49, a light transmissive display systemaccording to an embodiment of the invention is illustrated at 901. Thedisplay system 901 includes a light source 902, liquid crystal display903, such as that shown at 724 d in FIG. 43, optics 904, such as thatshown at 14 in FIG. 43, for projection or viewing of the images createdby the liquid crystal display, a computer control 905, such as thecontrol 729 in FIG. 43, and an image signal source 906, which may bepart of the control 905 or a separate source of video signals or othersignals as may be appropriate. A photodetector 907 also may be includedin the system 901.

[0291] The light source 902 may be one or more light emitting diodes,incandescent light source, fluorescent light source, light received viafiber optics or other means, a metal halide lamp, etc.

[0292] The liquid crystal display 903 may be a twisted nematic liquidcrystal cell, a variable birefringence liquid crystal cell, a supertwistliquid crystal cell, or some other type or liquid crystal cell able tomodulate light. The liquid crystal display 903 may include polarizers,wave plates, such as quarter wave plates or other wave plates, means forcompensating for residual birefringence or for problems encounteredduring off axis viewing, etc. Other types of display devices whichmodulate light as a function of some type of controlled input can beused in place of the liquid crystal cell 903. Exemplary liquid crystalcells and display devices which may be used for the liquid crystal cell903 are disclosed in U.S. Pat. Nos. 4,385,806, 4,436,376, 4,540,243, Re.32,521, and 4,582,396, which disclose surface mode and pi-cell liquidcrystal devices, and in concurrently filed, commonly owned U.S. patentapplication Ser. No. 08/187,050, entitled “Folded Variable BirefringenceLiquid Crystal Apparatus.”

[0293] The optics 904 may be one or more lenses separate from and/orincluded as part of the liquid crystal display for the purpose ofproviding an output image for viewing or for projection. If for viewing,such optics 904 may be one or more lenses which focus an image forclose, e.g., as in a head mounted display of the heads up display type,virtual reality type or multimedia type, or far viewing, e.g., as in aslide viewer or a television. If for projection, such optics 904 mayinclude projection optics which project an image formed by the display903 onto a screen for transmissive viewing or reflective viewing.

[0294] The image signal source 906 may be a source of computer graphicssignals, NTSC type television (video) signals, or other signals intendedto produce an image on the display 903. Such signals are decoded inconventional manner by the computer control 905, for example, as is thecase in many display systems, and in response to such decoding ordeciphering, the computer control 905 (or some other appropriatecontrol, circuit, etc.) operates the display 903 to produce desiredimages. If desired, the computer control 905 can operate the display 903in sequential manner to produce multiple images in sequence while thedisplay is being illuminated by only a single light source or color oflight, e.g., a monochromatic type of operation. Exemplary operation ofthis type is summarized in the above '396 patent. Other exemplary typesof operation of the computer control 905 include those employed inconventional liquid crystal display televisions of the hand-held orlarger type and/or liquid crystal type computer monitors. Alternatively,the computer control can operate the display 903 in a field sequentialor frame sequential manner whereby a particular image is formed inseveral parts; while one part is formed, the display is illuminated bylight of one color; while another part is formed, the display isilluminated by light of a different color; and so on. Using this fieldsequential type operation, multicolor images can be produced by thedisplay system apparatus 901.

[0295] In a typical input signal to a television or liquid crystaltelevision, there is information indicating brightness of the light tobe transmitted (or reflected) at a particular pixel. The computercontrol 905 is operative to compute the brightness information of aparticular image or scene and in response to such computation to controlthe intensity or brightness of the light source 902. While intensity orbrightness of the light source is controlled in this manner, thecomputer control 905 operates the liquid crystal display 903 to modulatelight without having to reduce the number of pixels used to transmitlight. Therefore, the full number or a relatively large number of pixelscan be used to form the image or scene even if the brightness of thescene as controlled by the controlled light source is relatively dark.

[0296] Information coming through from the image signal source 906 mayindicate various levels of illumination. There usually is a blankingpulse and a data line pulse. The computer control 905 can take theintegral of the data line electrically or an integral of the whole setof data (from all of the data lines of the scene) or all of the pixelswhile electrically skipping the blanking. Based on that integral, thebrightness of the light incident on the display 903 is controlled by thecomputer control 905. It will be appreciated that a person havingordinary skill in the art would be able to prepare an appropriatecomputer program to provide the integral functions and to use theresults of such integration to provide brightness control for the lightsource 902.

[0297] From the foregoing, then, it will be appreciated that theapparatus 901, including the computer control 905, is operative tocontrol or to adjust the brightness of a scene without degrading thecontrast ratio. Thus, the same contrast ratio can be maintained whilebrightness of a scene or image is adjusted. For example, the samecontrast ratio or substantially the same contrast ratio can bemaintained by the apparatus 901, whether depicting a scene of a brightsunlit environment or of the inside of a dark cave. Therefore, the scenewill have the appearance of illumination under natural illuminationconditions.

[0298] The features of the invention described below can be used invirtually any passive display system.

[0299] Power requirements of the apparatus 901 can be reduced over priordisplay systems because the intensity of light produced by the source902 is controlled to create dark images. In prior systems, though, theintensity of the light produced by the source was maintainedsubstantially constant while the amount of light permitted to betransmitted through the passive display would be reduced to create adark scene image.

[0300] In addition to controlling intensity of the light source 902 as afunction of brightness of a scene, the computer control 905 also may beresponsive to measurement or detection of the ambient environment inwhich the apparatus 901 is located. The brightness of such ambientenvironment may be detected by the photodetector 907. The photodetector907 may be place in a room or elsewhere where the image created by thedisplay 903 is to be viewed; and the brightness of the source 902 can beadjusted appropriately. For example, if the room is dark, it usually isdesirable to reduce brightness of the source; and if the room is brightor the apparatus is being used in sunlight, the brightness of the sourcemay be increased.

[0301] Turning to FIG. 50, a light reflective display system accordingto the invention is illustrated at 901′. The display system 901′includes a light source 902′, liquid crystal display 903′, optics 904′for projection or viewing of the images created by the liquid crystaldisplay 903′, a computer control 905′, and an image signal source 906. Aphotodetector 907 also may be included in the system 901. The variousparts of the display 903′ and optics 904′ may be the same or similar tothose disclosed in the U.S. patent applications referred to above. Thelight source 902′ and display 903′ may be of the type disclosed inconcurrently filed, commonly owned U.S. patent application Ser. No.08/187,262, entitled “Illumination System For A Display.”

[0302] For example, the light source 902′ may include a source ofcircularly polarized light 902 a′ and a cholesteric liquid crystalreflector 908. The liquid crystal display 903′ may be a reflectivevariable birefringence liquid crystal display device. Full Color FrameSequential Illumination System and Display.

[0303] Turning to FIG. 51 a full color display subsystem 919 includingillumination system 920 is shown. However, in the display subsystem 919the illumination system 920 includes several sources of light, eachhaving a different wavelength. For example, three separate light sources902 r, 902 g, 902 b provide red, green and blue wavelength light,respectively, or light that is in respective wavelength bands or rangesthat include red, green and blue, respectively. The light sources may berespective light emitting diodes or they may be other sources of red,green and blue light or other respective wavelengths of light, as may bedesired for use in the display subsystem 919. The cholesteric liquidcrystal reflector 908 is able to reflect green light; the reflector 908a is able to reflect red light; the reflector 908 b is able to reflectblue light. Such reflection occurs when the circular polarizationcharacteristic of the light is the same direction as the twist directionof the cholesteric liquid crystal material in the respective reflector.The reflectors 908, 908 a, 908 b are transparent to the otherpolarizations of incident light and to the other wavelengths of incidentlight.

[0304] The illumination system 920 is intended sequentially toilluminate the display 903′, which may include a wave plate, such as aquarter wave plate, (or respective portions of the display) withrespective wavelengths of light. For example, for a period of time thedisplay 903′ (or portion thereof) is illuminated with red light;subsequently illumination is by either green or blue light; and stillsubsequently illumination is by the other of green or blue light. Suchsequential illumination may be carried out sufficiently rapidly so thatrespective red, green and blue images created by the display 903′ whenilluminated by the respective colors of light are output from thedisplay subsystem 961 and are integrated by the human eye. As a result,the human eye effectively sees a multicolor image. Other examples offrame sequential switching to provide multicolor and/or full coloroutputs are known in the art. Various advantages inure to a framesequential multicolor display, including the ability to provide highresolution with approximately one-third the number of picture elementsrequired for a full color r, g, b display system in which respectivepixels are red, green or blue.

[0305] The sequential delivering of red, green and blue light to thedisplay 903′ is coordinated by the control system 905 with the drivingof the display 903′. Therefore, when a red image or a portion of a redimage is to be produced by the display 903′, it is done when red lightis incident on the display 903′; and the similar type of operationoccurs with respect to green and blue images.

[0306] If the respective light sources 902 r, 902 g, 902 b are lightemitting diodes, they may be sequentially operated or energized toprovide light in coordination with the operation of the display 903′under direct control and/or energization by the control system 905.Alternatively, the control system 905 may be coordinated with whateverother means are used to provide the respective red, green and blue colorlights of the light source.

[0307] Another example of frame sequential or field sequential operationof a displays subsystem like that shown at 961 herein is described inthe above-referenced patent applications. Another example of fieldsequential operation is described in U.S. Pat. No. 4,582,396, which ismentioned above and incorporated by reference.

[0308] Referring to FIG. 52, a head mounted display 960 includes a pairof display systems 961, 962 and a control system 705 for creating imagesintended to be viewed by the eyes 964, 965 of a person. The displaysystems 961, 962 may be positioned in relatively close proximity, forexample, at approximately one inch distance, to the respective eyes 964,965. A mounting mechanism, such as temple pieces 966, 967 and a nosebridge 968 may be provided to mount the display 960 on the head of theperson.

[0309] The control system 905 in conjunction with the display systems961, 962 are intended to create images for viewing by the eyes. Thoseimages may be monochromatic. The images may be multicolor. The imagesmay be two-dimensional or they may provide a three dimensional,stereoscopic effect. Stereoscopic effect viewing is obtained when thecontrol system 905 operates the display systems 961, 962 to provide,respectively, right eye and left eye images that are sufficientlydistinct to provide depth perception. Right eye, left eye imaging anddepth perception are techniques used in some stereoscopic imaging andviewing systems which are commercially available.

[0310] The display systems 961, 962 may be identical. The control system905 provides control and/or power input to the display systems 961, 962to create images for display to the eyes 964, 965. The display 960 maybe a head mounted display, such as a heads-up display, a virtual realitydisplay, or a multimedia display. The control system 905 may begenerally a control system of the type used in known head mounteddisplays to create such images. Such a control system may provide forcontrol of color, light intensity, image generating, gamma, etc. Thedisplay systems 961, 962 may include focusing optics so as to focus theimage created by the display systems for comfortable viewing, forexample from a few inches up to a few feet in front of the eyes, say,from about 20 inches to about several feet in front of the eyes.

[0311] It will be appreciated that the features of the liquid crystalcell 903′ may be used in the display 960 of the head mounted type. Also,features of the invention may also be employed in other types of displaysystems. One example is a display system that uses only a single displaysystem of the type described herein. Such display system may be locatedin proximity to an eye for direct viewing. Alternatively, such displaysystem may be used as part of a projection type display in which lightfrom the display system is projected onto a surface where the image isformed for viewing. Various lenses and/other optical components may beused to direct from the display system light to create an appropriateimage at a desired location.

[0312] Turning to FIGS. 53-58, operation of the apparatus is described.In FIG. 53 a plan view of a dot matrix liquid crystal display is shown.The shade of grey measured at several pixels is indicated. According tothe bottom graph in FIG. 53, the actual hade is shown; according to thedot matrix image at the side and top of FIG. 53, the actual shade of thepixel is shown. Thus, at location 1 on the graph at the bottom of FIG.53, there is a shade 2. At location 2, there is a shade 1. At location 3there is a shade 0, and so on. In pixel 1 marked in the top of FIG. 53,the pixel is a shade gray of 2; and at the adjacent pixel the pixel is ashade gray of 1, and so on. This is conventional. This would indicatethe signals coming in to the computer control 905.

[0313] In FIG. 54, an example of a bright image scene produced by backlight at a medium (normal) illumination level is illustrated at the top;the shades of gray are shown at the middle left; and the lamp lightlevel is constant at the bottom left. The viewer sees a bright/lowcontrast image of a person as seen at the top right of the drawing. Aside view of the display representing respective pixels and the traylevels thereof is shown at the bottom right of the figure.

[0314]FIG. 55 is similar to FIG. 54 again with average constant lamplight level. The average light level is produced; the average brightnessoutput from the display is to be produced; and the viewer sees anaverage brightness high contrast image because all conditions areoptimized.

[0315]FIG. 56 is similar to FIG. 54 again with average constant lamplight level and a dark transmission provided by the liquid crystal cell;the viewer sees a dim low contrast image.

[0316] FIGS. 54-56 represent operation of a standard display apparatus.FIGS. 57 and 58 represent applying the principles of the presentinvention to develop high contrast images. In FIG. 57 it is seen thatthere is the intent to produce a wide range of gray levels; and this ispossible by using a high intensity lamp level; the result is a brighthigh contrast image. In FIG. 58 it is intended that the viewer see a dimimage; the same range of grey shades are provided as is depicted in themiddle left graph of the drawing; but the lamp level is low. Therefore,there is a good contrast ratio provide to the viewer; from 0 to about 7at the brightness level shown in the graph at the upper left of thedrawing.

Conversion of Pixel Layout form Delta to Stripe Pattern by Time BaseMultiplexing of FIGS. 59-65

[0317] In color LC displays the complete color dot is generated by atriad of pixels. Three pixels, one red, one green, and one blue aregrouped together to form this triad. These pixels are commonly arrangedinto one of two geometric patterns, delta or stripe.

[0318] Referring to FIG. 59, in the delta arrangement 1000, two of thepixels of a triad 1001, say red 1002R and green 1002G will be locatednext to one another on the same pixel row 1003. The third pixel, sayblue 1002B, will be located on the next row 1004 down. The horizontalposition of the blue pixel 1002B will be halfway between its associatedred and green pixels 1002R, 1002G from the row above. The three pixels1002R, G, B of the triad 1001 may be referred to sometimes as a picturedot of the display 1005, which includes the delta arrangement 1000, suchas a television or some other type of display. By controlling theintensity of light from respective pixels of such a color dot or triad,the color of the output light or image viewed, projected or otherwiseused can be controlled. For illustration purposes a dotted border isdrawn around pixels from the same triad.

[0319] Referring to FIG. 60, in the stripe arrangement 1010, all threepixels 1011R, G, B are located side by side, on the same row 1012. Forillustration purposes a dotted border 1013 is drawn around pixels fromthe same triad in the display 1015 having the stripe arrangement 1010.

[0320] There is an important difference between the stripe 1010 anddelta 1000 patterns. In the stripe pattern 1010, the pixels 101R, G, Bof a triad 1012 are placed in vertical columns 1016, 1017, etc. All ofthe pixels in a single column are of a single color. In the deltapattern 1000, the pixels 1002R, G, B are not arranged in columns.Instead, alternate rows 1003, 1004, etc. are staggered. The pixels ofevery other row are displaced horizontally by one half of the pixelpitch. Pixels of a given color, say red, in one row are centered halfway between the red pixels of the row above and below. Thus the verticalarrangement of red pixels in a delta arrangement 1000 is a zigzag, oneand half pixel pitches wide, rather than a straight column.

[0321] Consider a delta pattern display 1005, a portion of which isrepresented by the delta arrangement 1000 of FIG. 59, and the videosignal, such as an interlaced NTSC signal, used to generate a picture onthat display. Displacement techniques, such as those disclosed aboveand/or in the above-mentioned patent applications, or other suchdisplacement techniques may be used to enhance the image output of thedisplay.

[0322] An example of a display system 1020, for example, including adisplay 1005 and an optical displacement system 1021, is depictedschematically in FIG. 61. The optical system 1021 includes in opticalseries an optical polarization switching device 1022, a birefringentdevice 1023, a further optical polarization switching device 1024, and afurther birefringent device 1025. In the illustrated example hereof theoptical polarization switching devices are liquid crystal cells whichare able selectively to rotate or not to rotate the plane ofpolarization of incident light a prescribed amount, for example, by 90°,depending on the energization conditions thereof. One example of such adevice is a birefringent liquid crystal cell, such as that sometimesreferred to in the art as a surface mode device (SMD) or a Pi Cell;examples of such devices are described above. The birefringent devices1023, 1025 may be, for example, calcite crystal material as is describedabove. Another material useful for such a birefringent device is lithiumniobate material. Plastic birefringent material or other birefringentmaterial alternatively may be used, an example being polyvinyl butyral.

[0323] The display 1005 may be a liquid crystal display, such as a TFT,active matrix, or some other type of display. Appropriate video and/orother driving circuitry (not shown), such as conventional NTSCtelevision circuitry, may be used to operate the display 1005. The lightoutput from the display 1005 to the optical displacement system 1021 isoptically polarized, for example, plane polarized. The display 1005 mayprovide light output which is plane polarized; alternatively oradditionally a plane polarizer 1026 may be located between the display1005 and the optical displacement system 1021. The axes and respectivearrangements of the components of the display system 1020 may begenerally as are described above with respect to the various otherembodiments of optical displacement systems, image doublers,quadruplers, dithering systems, etc., described above, any or all ofwhich may be included in the embodiment illustrated and described withrespect to FIGS. 61.

[0324] The optical displacement system 1021 may be used to displace theapparent location of pixels vertically by selected amounts. As oneexample, one of the birefringent devices 1023 or 1025 may be used toshift the pixels up one full pixel pitch distance. That is, the pixelsin row 1004 may be moved or switched up to the same vertical location asthe row 1003, i.e., they appear at the location of the row 1003. Theother birefringent device 1023 or 1025 may be used to shift the pixelsup one additional half pixel pitch distance. Alternatively, one or bothof the birefringent devices 1023, 1025 may effect downward verticalshifting of the apparent pixel locations.

[0325] Consider, then, as was mentioned just above, a delta patterndisplay 1005, a portion of which is represented by the delta arrangement1000 of FIG. 59, and the video signal, such as an interlaced NTSCsignal, used to generate a picture on that display. Suppose that thefirst raster line of picture information were removed from the videosignal. In this case, each raster line of picture information (data)will be displaced upward on the display 1005. Such data may be removed,for example, by simply eliminating it or by appropriately altering thehorizontal sync signal. It will now be presented on the pixel row whichis one above the row it was presented on for the unmodified version ofthe picture. Next, optically displace the entire picture down by adistance equal to one vertical pixel pitch is effected using the opticalsystem 1021. The technique for optical lateral displacement of imageshas been described elsewhere herein and in the above-mentioned patentapplications. The picture is now back in its original vertical position.But, the horizontal position of the pixels has changed. The pictureinformation is now displaced horizontally by a distance equal to one andone half times horizontal pixel pitch. The odd pixel rows are displacedin one direction, and the even pixel rows are displaced in the oppositedirection. FIG. 62 shows the new positions of the pixels (shaded),superimposed on the original pixel positions (unshaded). This process ortechnique may be referred to below as Vertically Generated HorizontalDisplacement or the VGHD technique for short.

[0326] As is shown schematically in FIG. 62, the VGHD technique can beused to double the pixel density, and thus the resolution, in thehorizontal direction. This is accomplished by using the VGHD techniqueon every other frame. The two views of the picture alternate at theframe rate. This usually will be fast enough to fuse them into a singleimage. Thus, two successive frames will be combined over time to act asa single super frame. This is time based multiplexing of a spatialpattern.

[0327] An example of the spatial doubling can be illustrated using FIG.62. When the VGHD (shaded) pixels are combined with the original pixels(unshaded) to form a composite picture, the result is a strip pixelpattern with twice the horizontal pixel density of the original deltapattern. The triads in the first half of this super frame will partiallyoverlap the triads in the second half of the super frame. This techniquecan be applied to either progressive or interlace scan formats. For theinterlace format, the first raster line should be removed from bothfields of each frame in which VGHD technique is applied.

[0328] VGHD doubling may be treated like any other active doubling stagefor example, as are described above. It can be combined with eitherpassive doubling or standard active vertical doubling as are describedabove. Passive doubling is performed in the standard way as is disclosedabove. A double refracting layer plus wave plate are placed in theoptical path downstream from all active doubling components. It providesspace fill to eliminate the “chicken wire” and to overlap the pixelcolors. Standard active vertical doubling requires an interlaced videoformat in conjunction with a display which has the same number of pixelrows as a single field of the video frame. The picture is opticallydisplaced down by a distance equal to one half the vertical pixel pitchon every other field. When the two fields are taken together as a singlefield, the number of pixels doubles, increasing the vertical resolution.There is no timing conflict between standard vertical doubling and VGHDdoubling, because standard vertical doubling operates at the field rateand VGHD doubling operates at the frame rate.

[0329] In FIG. 63 is shown a graph or chart showing exemplary timing foroperation of the optical system 1021 in conjunction with the display1005 of the display system 1020. The display system operates to providetwo frames 1030, e.g., an odd frame 1030I and an even frame 1030 e,sequentially. Each frame 1030 is comprised of two fields 1031, e.g., anodd field 1031 o and an even field 1031 e, sequentially. Along the graphportion 1032 is an indication of whether the first raster line isremoved (“Yes”) or not (“No”). The bottom graph 1033 of FIG. 63indicates the amount of displacement of the pixels by the optical system1021. For example, at time t₀ there is no shifting (displacement) ofpixel locations; at time t₁ the pixel locations are shifted verticallyby one half pixel pitch distance; at time t₂ the pixel locations areshifted vertically by one full pixel pitch distance; and at time t₃ thepixel locations are shifted 1½ ({fraction (3/2)}) pixel pitch distance.

[0330] Summarizing operation of the display system 1020 of FIG. 61,using the VGHD technique depicted in FIGS. 62 and 63, the objective isto obtain an increased number of RGB dots by doubling. Therefore, in row1000 of the display 1005 depicted in FIG. 62 there are twice as manytriads as there were in the row 1003 in the display 1005 as illustratedin FIG. 59 due to the optical shifting effected by the system 1021.Additionally, as will be described below, the space 1034 betweenadjacent rows, such as rows 1003, 1004 of the display 1005 as shown inFIG. 62, also can be filled in to increase image resolution as wasdescribed with respect to the various embodiments above.

[0331] In operation of the display system 1020, for example, then, thereare two sequential frames to compose a picture; and there are twosequential fields which comprise one frame.

[0332] In FIG. 63 at time t₀ graph 1030 indicates an odd frame 1003 o;graph 1031 indicates an odd field 1031 o; graph 1032 indicates that thefirst raster line is not removed; and graph 1033 indicates at 1033 athat there is no optical displacement of the image by the system 1021.

[0333] In FIG. 63 at time t₁, graph 1030 indicates an odd frame 1003 o;graph 1031 indicates an even field 1031 e; graph 1032 indicates that thefirst raster line is not removed; and graph 1033 indicates at 1033 bthat there is optical vertical displacement of the image by a distanceof ½ pixel pitch. This fills in the optical dead space in the area 1034,as was described above.

[0334] In FIG. 63 at time t₂, graph 1030 indicates an even frame 1003egraph 1031 indicates an odd field 1031 o; graph 1032 indicates that thefirst raster line is removed; and graph 1033 indicates at 1033 c thatthere is optical vertical displacement of the image by the system 1021by a distance equal to one full pixel pitch distance. In this case,since the first raster line is removed, this effectively shifts thepixels up one row; but the birefringent material 1023 or 1025 may beused to shift the pixel location down one full pixel pitch distance.This is represented by the locations of the shaded pixels in FIG. 62,for example. The first raster line can be removed, for example, byremoving a horizontal sync pulse associated with that line. In anyevent, the objective of the first raster line removal and the verticaldisplacement at time t₂ is to fill in the spaces between pixels in arow, such as row 1003, with pixels of the same triad but whichphysically are located in an adjacent row, such as row 1004. Thisdoubles the effective number of pixels, triads, and picture dots perrow.

[0335] In FIG. 63 at time t₃, graph 1030 indicates an even frame 1003 e;graph 1031 indicates an even field 1031 e; graph 1032 indicates that thefirst raster line is removed; and graph 1033 indicates at 1033 d thatthere is optical vertical displacement of the image by the system 1021by a distance equal to one and one half (1½ or {fraction (3/2)}) fullpixel pitch distance. (Such shifting is the combination of the fullpixel pitch distance shifting mentioned above at time t₂ and the ½ pixelpitch distance shift mentioned at time t₁. In this example, both shiftsare in the same direction; however, in an alternate embodiment theshifting could be respectively in opposite directions.) Such ½ pixelpitch distance shifting occurring at time t₃ may be carried out usingthe various shifting techniques mentioned above; and it is used, as attime t₁, to fill in the optical dead space 1034, for example.

[0336] Using the optical displacement system 1021 in the display system1020 of FIG. 61, the above-described operation of the system 1020 usingthe display 1005 can be carried out. For example, at respective timest₀, t₁, t₂ and t₃, respective signals to or energization of thepolarization rotating devices 1022, 1024 may be provided to effectdesired shifting or not of light from respective pixels and, thus, theapparent location of those pixels as viewed, as light therefrom isprojected to form an image, etc.

[0337] Referring to FIG. 64, several graphs 1040-1049 are illustratedshowing operation of the display system 1020, including the display 1005and the optical displacement system 1021. The graphs are similar tothose described above with respect to FIG. 63 and are labeledcorrespondingly with the graphs of FIG. 63 with reference to the system1020 of FIG. 61 and the display 1005 of FIG. 62.

[0338] Graphs 1048 a, 1049 a depict operation and delivery ofappropriate signals to the polarization rotating devices (SMD devices)1022, 1024 (FIG. 61) assuming birefringent material 1023 is the ½ pixelpitch distance image shifting birefringent material (e.g., calcite),i.e., is first in the optical path before the material 1025, whichprovides one full pixel pitch distance shifting function.

[0339] Graphs 1048 b, 1049 b depict operation and delivery ofappropriate signals to the polarization rotating devices (SMD devices)1022, 1024 (FIG. 61) assuming birefringent material 1023 is the one (1)full pixel pitch distance image shifting birefringent material (e.g.,calcite), i.e., is first in the optical path before the material 1025,which provides one half (½) pixel pitch distance shifting function.

[0340] In graph 1040 is shown respective odd and even frames. Graph 1041depicts respective odd and even fields. Graph 1042 represents whether ornot the first raster line of the field is removed. Graph 1043 indicatestotal vertical image displacement of respective rows of pixels, e.g., 0,½, 1 or {fraction (3/2)} pixel pitch distance. Graph 1044 representsdisplacement by the ½ pixel shifting calcite, either 1023 or 1025, andgraph 1045 represents displacement by the full pixel shifting calcite,the other of 1023 or 1025. Graphs 1046 and 1047 represent the directionof plane of polarization of light entering the respective birefringentmaterial 1023, 1025. Graphs 1048, 1049 represent the respective signals,low or high (maximum or minimum polarization rotation) of the respectiveSMD devices 1022, 1024.

[0341] In FIG. 65 the respective graphs are similar to those of FIG. 64,except there is a phase delay introduced. The phase delay, which isreferred to near the bottom of the figure as “SMD Phase Delay” helps toassure that the effect of operation of the SMD devices and the videosignals and operation of the display 1005 is optimal, e.g., beingoptimum at the center of the display. It is desirable for the SMDdevices to be in sync with the display when the video signal written tothe display is about one half way down the display. Another example ofphase delay or coordination technique is described in copending U.S.patent application Ser. No. 60/001972, filed Jul. 23, 1995, entitled,“Display Enhancement With Phase Coordinated Polarization Switching andMethod”, the entire disclosure of which hereby is incorporated byreference.

[0342] There is an alternative implementation of VGHD technique. In theabove-described description with respect to FIGS. 62-65, the firstraster line of the video frame was removed. This caused the picture tobe shifted up by one pixel row on the display. The picture was thenoptically returned to its original vertical position.

[0343] The alternative VGHD technique is applied to the same deltapattern 1000 display 1005 and the video signal used to generate apicture on that display. Instead of removing first raster line from thevideo signal, an extra raster line is added before the first line of theoriginal picture. This will be a “dummy” line containing no real pictureinformation. As a result, each raster line of the real pictureinformation will be displaced downward on the display 1005. It will nowbe presented on the pixel row which is one below the row it waspresented on for the unmodified version of the picture. Next, using theoptical system 1021, for example, optically displace the entire pictureback up by a distance equal to one vertical pixel pitch. The picture isnow back in its original vertical position, but the horizontal positionof the of the pixels has again shifted. The picture information is nowdisplaced horizontally by a distance equal to one and one half timeshorizontal pixel pitch. The odd pixel rows are displaced in onedirection, and the even pixel rows are displaced in the oppositedirection. This pattern of horizontal pixel shift is identical to thatproduced by the original VGHD technique described above with respect toFIGS. 62-65. This is true everywhere on the display except for the topand bottom pixel rows. In the original technique above, the bottom rowof the display remained blank. (Because one raster line had beenremoved, the display runs out of picture information at the last row.)In the alternative VGHD technique here, it is the top row of the displaywhich remains blank. As a result, when the VGHD technique is used forhorizontal doubling, the bottom line in the above-described techniqueand the top line in the alternative technique will not be doubled.

[0344] The addition or removal of raster lines from the video signal canbe implemented by adding or removing horizontal sync pulses. If thehorizontal sync pulse is suppressed for a given raster line, then thedisplay will simply ignore the video data for that line. It is thereforenot presented on the display. When a raster line is added by addinghorizontal sync pulse, it needs to be timed properly. Each video formathas a specific horizontal scan frequency (15.7 kHz for NTSC, 31.4 kHzfor VGA). The proper time between horizontal sync pulses is simply theinverse of that frequency. To add a dummy raster line to the beginningof a video frame, add the new sync pulse during the vertical blanking ata point in time equal to one horizontal scan time before the firsthorizontal sync pulse of that frame.

[0345] Summarizing operation of the invention described with respect toFIGS. 59-65, then, video line removal at the first row of pixels or linecan be used to shift the picture up on the display. To counter thatshift, the optical system 1021 may be used to shift the rows of pixels 1full pixel pitch distance down; this provides horizontal doubling of thetype depicted in FIG. 62, for example. Thus, “horizontal doubling” iseffected by a vertical displacing or shifting of the images of thepixels in respective rows thereof. Timing of the system 1021 to carryout such horizontal doubling may be in accordance with the Graphs ofFIGS. 6365, for example.

[0346] It is possible to add to such horizontal doubling a verticaldoubling function for the purpose of covering some or all of the opticaldead space 1034 (FIG. 62). Such vertical doubling can displace or shiftthe respective pixels into the space 1034 using the optical system 1021and/or various of the above-described optical systems described earlierin this application. Timing of the system 1021 to carry out suchvertical doubling may be in accordance with the Graphs of FIGS. 63-65,for example.

What is claimed is:
 1. A method of displaying an image, comprising:displaying an unshifted image in a first time interval between a time t₀and a time t₁; displaying a first shifted image in a second timeinterval between the time t₁ and a time t₂, wherein the first shiftedimage is vertically displaced by one-half of a pixel height relative tothe unshifted image; displaying a second shifted image in a third timeinterval between the time t₂ and a time t₃, wherein the second shiftedimage is vertically displaced by the pixel height relative to theunshifted image; and displaying a third shifted image in a fourth timeinterval between the time t₃ and a time t₄, wherein the second shiftedimage is vertically displaced by one and one-half times the pixel heightrelative to the unshifted image; wherein the shifted images are shiftedby selectively sending signals to a one-pixel-height polarizationrotating device and to a one-half-pixel height polarization rotatingdevice, and wherein the polarization rotating devices are calcitecrystals.